Fetch the pickme branch being checked

Now that git SHA verification is ls-remote based and not fetch based, branches
that are pickme'd are not in the local git repository. This causes problems for
merges.
Merge pull request #96 from rschlaikjer/fetch-pickmes-when-checking

Fetch the pickme branch being checked

Now that git SHA verification is ls-remote based and not fetch based, branches
that are pickme'd are not in the local git repository.