Refactored methods which dealed directly with gridfile contents instead of using gridfile object. This refactoring is needed in order to later refactore pre and post processing of chunks logic to optimize buffer allocation and prepare the ground for effective usage of pre and post processing for encryption, which requires keeping a context between calls
Added tests for return value of gridfile_write_buffer and added comments of return value on gridfs.h
GFS_INIT missing from test_random_write
Merge remote-tracking branch 'refs/remotes/Mongo/master' into master-pull-refactor-newgridfs

Conflicts:
	src/gridfs.c
	src/gridfs.h
Fixed some minor issue to allow compilation on Visual Studio
Merge pull request #113 from jsbattig/master-pull-refactor-newgridfs

Refactored methods which dealed directly with gridfile contents instead ...
Merge branch 'refs/heads/official' into bson_finished_data_check_size