vector: Timsort all of the things

Drop the GLibc implementation of Merge Sort and replace it with Timsort.

The algorithm has been tuned to work on arrays of pointers (void **),
so there's no longer a need to abstract the byte-width of each element
in the array.

All the comparison callbacks now take pointers-to-elements, not
pointers-to-pointers, so there's now one less level of dereferencing.

E.g.

	 int index_cmp(const void *a, const void *b)
	 {
	-	const git_index_entry *entry_a = *(const git_index_entry **)(a);
	+	const git_index_entry *entry_a = (const git_index_entry *)(a);

The result is up to a 40% speed-up when sorting vectors. Memory usage
remains lineal.

A new `bsearch` implementation has been added, whose callback also
supplies pointer-to-elements, to uniform the Vector API again.

src/config.c

@@ -56,8 +56,8 @@ void git_config_free(git_config *cfg)
 
 static int config_backend_cmp(const void *a, const void *b)
 {
-	const file_internal *bk_a = *(const file_internal **)(a);
-	const file_internal *bk_b = *(const file_internal **)(b);
+	const file_internal *bk_a = (const file_internal *)(a);
+	const file_internal *bk_b = (const file_internal *)(b);
 
 	return bk_b->priority - bk_a->priority;
 }

src/index.c

@@ -109,31 +109,31 @@ static int write_index(git_index *index, git_filebuf *file);
 int index_srch(const void *key, const void *array_member)
 {
 	const char *filename = (const char *)key;
-	const git_index_entry *entry = *(const git_index_entry **)(array_member);
+	const git_index_entry *entry = (const git_index_entry *)(array_member);
 
 	return strcmp(filename, entry->path);
 }
 
 int index_cmp(const void *a, const void *b)
 {
-	const git_index_entry *entry_a = *(const git_index_entry **)(a);
-	const git_index_entry *entry_b = *(const git_index_entry **)(b);
+	const git_index_entry *entry_a = (const git_index_entry *)(a);
+	const git_index_entry *entry_b = (const git_index_entry *)(b);
 
 	return strcmp(entry_a->path, entry_b->path);
 }
 
 int unmerged_srch(const void *key, const void *array_member)
 {
 	const char *path = (const char *) key;
-	const git_index_entry_unmerged *entry = *(const git_index_entry_unmerged **) (array_member);
+	const git_index_entry_unmerged *entry = (const git_index_entry_unmerged *)(array_member);
 
 	return strcmp(path, entry->path);
 }
 
 int unmerged_cmp(const void *a, const void *b)
 {
-	const git_index_entry_unmerged *info_a = *(const git_index_entry_unmerged **)(a);
-	const git_index_entry_unmerged *info_b = *(const git_index_entry_unmerged **)(b);
+	const git_index_entry_unmerged *info_a = (const git_index_entry_unmerged *)(a);
+	const git_index_entry_unmerged *info_b = (const git_index_entry_unmerged *)(b);
 
 	return strcmp(info_a->path, info_b->path);
 }

src/odb.c

@@ -223,8 +223,8 @@ static int init_fake_wstream(git_odb_stream **stream_p, git_odb_backend *backend
 
 static int backend_sort_cmp(const void *a, const void *b)
 {
-	const backend_internal *backend_a = *(const backend_internal **)(a);
-	const backend_internal *backend_b = *(const backend_internal **)(b);
+	const backend_internal *backend_a = (const backend_internal *)(a);
+	const backend_internal *backend_b = (const backend_internal *)(b);
 
 	if (backend_a->is_alternate == backend_b->is_alternate)
 		return (backend_b->priority - backend_a->priority);

src/odb_pack.c

@@ -699,8 +699,8 @@ static int pack_index_open(struct pack_file *p)
 
 static int packfile_sort__cb(const void *a_, const void *b_)
 {
-	struct pack_file *a = *((struct pack_file **)a_);
-	struct pack_file *b = *((struct pack_file **)b_);
+	struct pack_file *a = (struct pack_file *)a_;
+	struct pack_file *b = (struct pack_file *)b_;
 	int st;
 
 	/*

src/refs.c

@@ -825,8 +825,8 @@ static int packed_remove_loose(git_repository *repo, git_vector *packing_list)
 
 static int packed_sort(const void *a, const void *b)
 {
-	const git_reference *ref_a = *(const git_reference **)a;
-	const git_reference *ref_b = *(const git_reference **)b;
+	const git_reference *ref_a = (const git_reference *)a;
+	const git_reference *ref_b = (const git_reference *)b;
 
 	return strcmp(ref_a->name, ref_b->name);
 }

src/tree.c

@@ -40,7 +40,7 @@ static int valid_attributes(const int attributes) {
 int entry_search_cmp(const void *key, const void *array_member)
 {
 	const char *filename = (const char *)key;
-	const git_tree_entry *entry = *(const git_tree_entry **)(array_member);
+	const git_tree_entry *entry = (const git_tree_entry *)(array_member);
 
 	return strcmp(filename, entry->filename);
 }
@@ -53,8 +53,8 @@ static int valid_attributes(const int attributes) {
 
 int entry_sort_cmp(const void *a, const void *b)
 {
-	const git_tree_entry *entry_a = *(const git_tree_entry **)(a);
-	const git_tree_entry *entry_b = *(const git_tree_entry **)(b);
+	const git_tree_entry *entry_a = (const git_tree_entry *)(a);
+	const git_tree_entry *entry_b = (const git_tree_entry *)(b);
 
 	return git_futils_cmp_path(entry_a->filename, strlen(entry_a->filename),
                                   entry_a->attr & 040000,