Bug 702584 - \cite rejects valid BibTeX keys

According to the documentation the .bib is automatically added to the names in the CITE_BIB_FILES. In the example given with this bug this was not the case.
In case CITE_BIB_FILES was set to 'my.bib' it was working, but with only 'my' it wasn't.
Merge pull request #186 from albert-github/feature/bug_702584

Bug 702584 - \cite rejects valid BibTeX keys