FIX: Check file exist when attempting upload.

Both "page.uploadFile()" and "onFilePicker = function() {}" check file exists before accepting them.
If file don't exists, they are "ignored".

Fixes issue #941: https://code.google.com/p/phantomjs/issues/detail?id=941
FIX: 'resource request errors' close the server.

The test "should handle resource request errors"
was not closing the server at the end of the test,
interfering with the successive tests.
Fixing up indentation for our Jasmine test specs.

Just getting rid of an itch of mine.
Update ChangeLog.

http://code.google.com/p/phantomjs/issues/detail?id=939