Make references to linked JIRA issues case insensititve (BB-8420)

Hi there,

I set up a self-hosted JIRA instance, which I linked with a bitbucket team account using the DVCS connector plugin.
Linking commits with JIRA issues works perfectly, but there is one small drawback: bitbucket only seems to recognize the reference to an attached JIRA when the issue key is written perfectly in uppercase letters. In case only one letter is lowercase (which happens easily in the heat of the moment), there is no link to JIRA on bitbucket. Yet the commit appears in JIRA's commits section.
I guess it's an easy thing for you to fix this. On the other hand, it would make bitbucket feel more consistent.

Thanks in advance!