CRC32 collision issue

[BenceSzalai]

The phpThumbOf::createThumbnail() method uses the name of the resizer, the time the image was uploaded, the original filename, phpThumb options and the remote url, if any to generate the CRC part of the cached image filename.

I've just ran into a situation, when all these matched, and one image started to overwrite another. Lost some hair until I've figured out what was going on.

Suggestion:
Add file size to $modflags after phpthumbof.class.php#L321. Something like this:

$modflags .= filesize($this->input);

Or even better, to completely eliminate the issue, even when file sizes match: use the full path of the original image instead of the filename only. This can be done easily by using this instead of line 307 of phpthumbof.class.php

$hashExtras = $this->input;

Let me know if you'd like a PR!