Fix basedir error for the validate diff resource.
Review Request #7127 — Created March 26, 2015 and submitted — Latest diff uploaded
When trying to post against a repository that requires a base directory and not
providing it, the resulting error was being split into a list of characters.
This was happening because we were returning a string as the error instead of a
list, so iterating over it was turning it into a list.
Verified that the error was presented as a readable string instead of a list of
individual characters.