chore(client/js/s3/policysignature.ajax.requester.js): XHR is not used directly in this requester
feat(client/js/ajax.requester.js): #898 - various improvements to facilitate S3 MPU REST calls

- Account for lack of a default Content-Type (dynamic Content-Type)
- If there are no params to send, don't send content at all
 -Allow for on-demand headers
feat(Gruntfile.coffee): #898 - reference ajax requester for initiating S3 MPU requests
feat(client/js/s3/handler.xhr.js): #898 - start of chunked upload support for S3 uploader
feat(client/js/s3/multipart.initiate.ajax.requester.js): #898 - Functional "Initiate Multipart Upload" ajax request transport
feat(client/js/s3/policysignature.ajax.requester.js): #898 - allow policy and REST request headers to be submitted for signature
feat(client/js/s3/uploader.basic.js): #898 - minimum chunk size for S3 MPU requests is 5 MB
test(test/fineuploader/S3Uploads.java): #898 - sign MPU requests as well
refactor(client/js/s3/policysignature.ajax.requester.js): #898 - pending signature container is more of an object
feat(client/js/s3/multipart.initiate.ajax.requester.js): #898 - functional "Initiate MPU" ajax requester

- Comments
- Passes the uploadId to the xhr handler on success.
refactor(client/js/ajax.requester.js): #898 - Allow caller to specify body for request

The ajax requester base module is getting a bit hairy.  I will need to spend some time rethinking the API
and the logic used to determine the parameters and the body of the request.
feat(client/js/s3/multipart.abort.ajax.requester.js): #898 - Stub for S3 abort REST calls

These types of requests will need to be sent when an in-progress upload is cancelled.
feat(client/js/s3/multipart.complete.ajax.requester.js): #898 - S3 Complete Multipart REST call transport

These types of requests will need to be sent after we send the last part of a file.  This instructs
AWS to combine all of the parts and response when the file has been created.
refactor(form & xhr handlers): #898 - renames & spacing issues
feat(client/js/s3/handler.xhr.js): #898 - start of support for chunking
feat(client/js/s3/signature.ajax.requester.js): #898 - rename file & constructor
feat(client/js/s3/multipart.initiate.ajax.requester.js): #898 - comments and minor adjustments
feat(Gruntfile.coffee): #898 - reference multipart requesters, rename initiate requester
refactor(ajax requester): remove code duplication
docs(client/js/s3/multipart.complete.ajax.requester.js): #899 - comments