Description:
------------
When calling touch() on a plain path, the stat cache doesn't get cleared. However, when calling touch() on a 'file://' URL, the stat cache gets cleared by virtue of `php_plain_files_metadata` which clears the stat cache after all operations.

This leads to the behaviour as shown in the test script (output available here: https://3v4l.org/0VQIo)

Furthermore: fopen(), fwrite(), fclose() does not clear the stat cache in either case and neither does file_put_contents().

I would create a PR to fix the touch() case, but in general, it's probably worth reconsidering the usefulness of the stat-cache these days. Even over an NFS link, when doing nothing but stat()'ing, you still only lose about 10% performance if you call clearstatcache() after every stat().

Plus, the cache really only helps when you continuously stat() the same file within the same request, which probably isn't correct application behaviour anyways.

So in general, I would propose to actually kill the stat cache which would fix this inconsistency as well :-)

Test script:
---------------
<?php

// doesn't update realpath cache
touch('/tmp/foo');
var_dump(filemtime('/tmp/foo'));
touch('/tmp/foo', 1);
var_dump(filemtime('/tmp/foo'));

// does update the realpath cache
touch('file:///tmp/foo');
var_dump(filemtime('file:///tmp/foo'));
touch('file:///tmp/foo', 1);
var_dump(filemtime('file:///tmp/foo'));

Expected result:
----------------
int(1469202653)
int(1)
int(1469202653)
int(1)

Actual result:
--------------
int(1469202653)
int(1469202653)
int(1469202653)
int(1)