Fix _has_hgsubversion to handle OSError.
Fix _has_hgsubversion to handle OSError.

In the case that running 'hg svn ...' fails with an OSError, we want to skip
tests rather than failing. Trivial change.

beol/rbtools,beol/rbtools,beol/rbtools,datjwu/rbtools,haosdent/rbtools,datjwu/rbtools,reviewboard/rbtools,davidt/rbtools,haosdent/rbtools,davidt/rbtools,halvorlu/rbtools,halvorlu/rbtools,datjwu/rbtools,halvorlu/rbtools,davidt/rbtools,reviewboard/rbtools,reviewboard/rbtools,haosdent/rbtools