Merge branch 'ar/diff-args-osx-precompose'

Many commands normalize command line arguments from NFD to NFC
variant of UTF-8 on OSX, but commands in the "diff" family did
not, causing "git diff $path" to complain that no such path is
known to Git.  They have been taught to do the normalization.

* ar/diff-args-osx-precompose:
  diff: run arguments through precompose_argv

builtin/diff.c

@@ -320,6 +320,7 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		gitmodules_config();
 	init_diff_ui_defaults();
 	git_config(git_diff_ui_config, NULL);
+	precompose_argv(argc, argv);
 
 	init_revisions(&rev, prefix);