hghave: check darcs version more strictly test-convert-darcs.t suddenly started failing on my Debian sid machine. The reason was Darcs was upgraded from 2.12.0 to 2.12.4 so the original pattern got to match the last two digits. Fix the pattern to match 2.2+.

tests: silence output of darcs command It appears darcs is more verbose by default these days. I got test failure with Darcs 2.12.4.