Update sbt's PGP support for the plugin used by sbt 0.13.
Remove some warnings around case-matching exceptions in Scala 2.10.

Scala 2.10 doesn't like catchalls that catch all Throwables, so we
change our exception catches to catch Exceptions only.
Merge remote-tracking branch 'farmdawg/up-the-grade'
Release 0.4 with sbt 0.13 support.