Full rework of quote_c_style and write_name_quoted.

* quote_c_style works on a strbuf instead of a wild buffer.
* quote_c_style is now clever enough to not add double quotes if not needed.

* write_name_quoted inherits those advantages, but also take a different
  set of arguments. Now instead of asking for quotes or not, you pass a
  "terminator". If it's \0 then we assume you don't want to escape, else C
  escaping is performed. In any case, the terminator is also appended to the
  stream. It also no longer takes the prefix/prefix_len arguments, as it's
  seldomly used, and makes some optimizations harder.

* write_name_quotedpfx is created to work like write_name_quoted and take
  the prefix/prefix_len arguments.

Thanks to those API changes, diff.c has somehow lost weight, thanks to the
removal of functions that were wrappers around the old write_name_quoted
trying to give it a semantics like the new one, but performing a lot of
allocations for this goal. Now we always write directly to the stream, no
intermediate allocation is performed.

As a side effect of the refactor in builtin-apply.c, the length of the bar
graphs in diffstats are not affected anymore by the fact that the path was
clipped.

Signed-off-by: Pierre Habouzit <madcoder@debian.org>

builtin-ls-tree.c

@@ -112,10 +112,8 @@ static int show_tree(const unsigned char *sha1, const char *base, int baselen,
 			       abbrev ? find_unique_abbrev(sha1, abbrev)
 			              : sha1_to_hex(sha1));
 	}
-	write_name_quoted(base + chomp_prefix, baselen - chomp_prefix,
-			  pathname,
-			  line_termination, stdout);
-	putchar(line_termination);
+	write_name_quotedpfx(base + chomp_prefix, baselen - chomp_prefix,
+			  pathname, stdout, line_termination);
 	return retval;
 }