Name make_*_path functions more accurately

Rename the make_*_path functions so it's clearer what they do, in
particlar make clear what the differnce between make_absolute_path and
make_nonrelative_path is by renaming them real_path and absolute_path
respectively. make_relative_path has an understandable name and is
renamed to relative_path to maintain the name convention.

The function calls have been replaced 1-to-1 in their usage.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -397,7 +397,7 @@ int set_shared_perm(const char *path, int mode)
 	return 0;
 }
 
-const char *make_relative_path(const char *abs, const char *base)
+const char *relative_path(const char *abs, const char *base)
 {
 	static char buf[PATH_MAX + 1];
 	int i = 0, j = 0;