Calculate the Windows user profile directory the same way as msysgit

On most systems %USERPROFILE% is the same as %HOMEDRIVE%\%HOMEPATH%,
however, for windows machines in an AD or domain environment this
might be different and %HOMEDRIVE%\%HOMEPATH% seems to be better.

Signed-off-by: Sven Strickroth <email@cs-ware.de>

src/fileops.c

@@ -469,7 +469,7 @@ int git_futils_find_global_file(git_buf *path, const char *filename)
 		}
 	}
 
-	if (win32_expand_path(&root, L"%USERPROFILE%\\") < 0 ||
+	if (win32_expand_path(&root, L"%HOMEDRIVE%\\%HOMEPATH%\\") < 0 ||
 		root.path[0] == L'%') /* i.e. no expansion happened */
 	{
 		giterr_set(GITERR_OS, "Cannot locate the user's profile directory");