Merge pull request #199 from ktf/master

Allow running even without a PR for an external.
Add CMSSW_7_3_0_pre2_DEVEL for slc6_amd64_gcc481 as .
use gcc491 as production arch for 73x
Merge pull request #200 from smuzaffar/master

use gcc491 as production arch for 73x
Add amagitte as watcher.

Fix cms-sw/cms-bot#6430.