Prefer perfect uid matches in keyselection combo

The idea here is that if there are keys like:

tom-store@abc.com
susi-store@abc.com
store@abc.com

And the user wants to send a mail to "store@abc.com"
the filter should still show tom and susi (because they
both are part of store) but the key for "store" should
be preselected.

• GnuPG-Bug-Id: T3978