Bugfix tests

- Fix typo in Overlap Error (Closes JIRA CBDEUCE-211)
- Fix upload block should return X-Block-Reference-Count and X-RefModified (Closes JIRA CBDEUCE-255)
- Fix bug in Block Collection on_post, error message specified PUT instead of POST
Just wondering about this.
How could _count_ be None? If either files_cnt or fileblocks_cnt is None, then the + operand will fail and you'll get an exception.
If files_cnt and fileblocks_cnt are already verified to be numbers, is there a problem with just returning _count_ ?