internal cleanup: excise is_file_readable.

This was an awful, ancient function. This is exactly what the
isreadable(path) function does, so there's no need for this. Also,
in most of the places we were calling it, skipping over files that
exist but are not readable is unhelpful – it would be better to
fail and let the user know that a file that was in the lookup path
and *should* be readable isn't. Arguably, we should even weaken the
test to just `ispath` and fail if the thing exists but is not a
regular file and is, say, a directory unexpectedly.

base/client.jl

@@ -216,11 +216,7 @@ function parse_input_line(io::IO)
 end
 
 # try to include() a file, ignoring if not found
-function try_include(f::String)
-    if is_file_readable(f)
-        include(f)
-    end
-end
+try_include(path::String) = isfile(path) && include(path)
 
 function process_options(args::Array{Any,1})
     global ARGS, bind_addr

base/loading.jl

@@ -1,10 +1,5 @@
 # require
 
-function is_file_readable(path::String)
-    s = stat(bytestring(path))
-    return isfile(s) && isreadable(s)
-end
-
 function find_in_path(name::String)
     isabspath(name) && return name
     isfile(name) && return abspath(name)
@@ -17,11 +12,11 @@ function find_in_path(name::String)
     end
     for prefix in [Pkg.dir(), LOAD_PATH]
         path = joinpath(prefix, name)
-        is_file_readable(path) && return abspath(path)
+        isfile(path) && return abspath(path)
         path = joinpath(prefix, base, "src", name)
-        is_file_readable(path) && return abspath(path)
+        isfile(path) && return abspath(path)
         path = joinpath(prefix, name, "src", name)
-        is_file_readable(path) && return abspath(path)
+        isfile(path) && return abspath(path)
     end
     return nothing
 end

base/sysimg.jl

@@ -351,7 +351,7 @@ precompile(println, (TTY,))
 precompile(print, (TTY,Char))
 precompile(==, (Bool,Bool))
 precompile(try_include, (ASCIIString,))
-precompile(is_file_readable, (ASCIIString,))
+precompile(isfile, (ASCIIString,))
 precompile(include_from_node1, (ASCIIString,))
 precompile(source_path, (Nothing,))
 precompile(task_local_storage, ())

base/util.jl

@@ -136,18 +136,11 @@ end
 # source files, editing
 
 function find_source_file(file)
-    if file[1]!='/' && !is_file_readable(file)
-        file2 = find_in_path(file)
-        if file2 != nothing
-            return file2
-        else
-            file2 = "$JULIA_HOME/../share/julia/base/$file"
-            if is_file_readable(file2)
-                return file2
-            end
-        end
-    end
-    return file
+    (isabspath(file) || isfile(file)) && return file
+    file2 = find_in_path(file)
+    file2 != nothing && return file2
+    file2 = "$JULIA_HOME/../share/julia/base/$file"
+    isfile(file2) ? file2 : nothing
 end
 
 function edit(file::String, line::Integer)