GridFS streams do not yet support seeking (PHPLIB-213), and HHVM requires a stream_seek() implementation in order to pass a non-negative offset to stream_get_contents().

HHVM does not support comparing ObjectIDs with the equality operator (i.e. `==`). For documents, which may contain arbitrary BSON types, converting to JSON is the easiest solution. The documents will then be compared as extended JSON and produce a readable diff on error.

Remove MongoDB 2.4 from the build matrix and use the latest stable driver by default.

Add explicit jobs to test MongoDB 2.4, driver 1.1.0 (oldest supported version), and the latest unstable driver version. Lastly, restrict PHP 5.4 and 5.5 to a single job each.

PhpStorm (and possibly other IDEs) must be able to resolve the class name in order to process these references. We can use FQCNs instead of adding "use" statements.

As a rule of thumb, we've decided keep all optional parameters in an options array across the library's public API.

This adds Bucket::getFileDocumentForStream() and Bucket::getFileIdForStream() methods, the latter of which was renamed from getIdFromStream().

Additionally, this replaces the getId() method in both internal stream classes with a getFile() method. The debug output for ReadableStream has also been simplified to include the entire file document instead of ID, chunkSize, and length.