GridFS: Eventually `gridfile_writer_init` should return a meaningful value
Minor refactoring and compilation fixes
GridFS: Stop writing when encountering an error
Tests: Add macro for gridfs_init
GridFS: Add return value to gridfs_remove_filename
Merge branch 'refs/heads/official' into gridfs_changes

Conflicts:
	test/gridfs_test.c
Merge pull request #118 from noa--/gridfs_changes

Minor GridFS changes