imagefield 6.x-3.8

The 3.8 release of ImageField is being released to match the 3.8 version of FileField. Both modules should be updated at the same time. The 3.8 version of FileField fixes a major problem that would prevent Google Chrome users from being able to upload a file. This version of ImageField also fixes several minor bugs.

Bug fixes:
#939102: Accept attribute contains extensions instead of mimetypes (preventing Chrome from selecting files) (fixed in tandem with FileField)
#786286: Default thumbnail lost on validation errors on field settings page.
#501594: Default image incorrectly deleted when replaced on a shared content type
#931540: Images have wrong path when using private files and absolute Windows file directory