bolt-gen: add 'top-line' file comments to output

if there are any comments that aren't "attached" to a message,
print them at the top of the generated file. we need this for
the fancy auto-gen'd dependencies in the tool-wiregen tests.

tools/gen/impl_template

@@ -6,8 +6,11 @@
 #include <ccan/mem/mem.h>
 #include <ccan/tal/str/str.h>
 #include <stdio.h>
-
+% for comment in top_comments:
+/*${comment} */
+% endfor
 % for enum_set in enum_sets:
+
 const char *${enum_set['name']}_name(int e)
 {
 	static char invalidbuf[sizeof("INVALID ") + STR_MAX_CHARS(e)];
@@ -29,7 +32,7 @@ const char *${enum_set['name']}_name(int e)
 % for subtype in subtypes:
 /* SUBTYPE: ${subtype.name.upper()} */
     % for c in subtype.type_comments:
-/* ${c} */
+/*${c} */
     % endfor
 <% static = '' if options.expose_subtypes else 'static ' %>
 ${static}void towire_${subtype.name}(u8 **p, const struct ${subtype.name} *${subtype.name})
@@ -38,10 +41,9 @@ ${static}void towire_${subtype.name}(u8 **p, const struct ${subtype.name} *${sub
 	${f.type_obj.type_name()} ${f.name} = tal_count(${subtype.name}->${f.len_field_of});
 	% endfor
 
-## FIXME: abstract this out? (semi-shared with towire_msg, minus the optional bits)
 	% for f in subtype.fields.values():
 	    % for c in f.field_comments:
-	/* ${c} */
+	/*${c} */
 	    % endfor
 <%
     fieldname = '{}->{}'.format(subtype.name,f.name)

tools/generate-bolts.py

@@ -33,9 +33,7 @@ def next_line(args, lines):
         lines = fileinput.input(args)
 
     for i, line in enumerate(lines):
-        if not bool(line.strip()):
-            continue
-        yield i, line.strip()
+        yield i + 1, line.strip()
 
 
 # Class definitions, to keep things classy
@@ -285,6 +283,10 @@ class Master(object):
     messages = {}
     extension_msgs = {}
     inclusions = []
+    top_comments = []
+
+    def add_comments(self, comments):
+        self.top_comments += comments
 
     def add_include(self, inclusion):
         self.inclusions.append(inclusion)
@@ -362,6 +364,7 @@ def write(self, options, output):
                 'set': tlv.messages.values(),
             })
         stuff = {}
+        stuff['top_comments'] = self.top_comments
         stuff['options'] = options
         stuff['idem'] = re.sub(r'[^A-Z]+', '_', options.header_filename.upper())
         stuff['header_filename'] = options.header_filename
@@ -388,6 +391,12 @@ def main(options, args=None, output=sys.stdout, lines=None):
             ln, line = next(genline)
             tokens = line.split(',')
             token_type = tokens[0]
+
+            if not bool(line):
+                master.add_comments(comment_set)
+                comment_set = []
+                continue
+
             if token_type == 'subtype':
                 subtype, _ = master.add_type(tokens[1])