Merged pull request #271
Fixed PHP-672: MongoGridFSFile::write() leaks memory

return_value seems to have been just a handy variable to use here, but
its really confusing as its later overwritten with a long, without
freeing the previously assigned data.
Using a real temp variable fixes the leak
Add test for PHP-672
Fixed test title.
Merged pull request #275
Fixed PHP-385: GridFS::storeFile with a string argument for 2Gb files

ftell() returns long, not int :)
Don't really want to make a 2gb testfile for this and creating one
on-the-fly would be really annoying and unexpected memory usage and
requirement from the test suite
Fixed CS in new code.
Merged pull request #277
Fixed PHP-676: Collection level write concern overwritten by deprecated "safe" option
Merged pull request #278
Fixed PHP-586: GridFS should only do one GLE

Removed this forced acknowledged behaviour so its now actually up to the
user what he wants to do.

We do however now execute one GLE at the end of writing all the chunks
to guarantee that we have written all the data before saving the
metadata and filemd5
Fixed CS.
Merged pull request #280
Fixed PHP-658: Add error codes for GridFSExceptions