consider all xhr 2xx statuses to be success

Previously only status of 200 was considered
success, so 201-204 would trigger onError.
Now use regex test to verify status == /2\d\d/.
allow extraFields to be a function
Refactored to allow manual upload trigger from HTML5 file drop event
small cleanup
Localize scope of 'event' when looping over 'available_events' to fix in IE10
Fixed encoding problems X-File-Name header

When non-ascii chars are presents in file name, a TypeError exception is thrown.
Merge remote-tracking branch 'remotes/maosmurf/master'
Merge remote-tracking branch 'remotes/gunjanpatidar/master'
Merge remote-tracking branch 'remotes/inertialbit/master'
only accept HTTP 200..204 as okay
Merge remote-tracking branch 'remotes/theoephraim/master'