color the build yellow when any PHP warnings are seen

* Fixes #1135
* Jenkins: http://jenkins.buttonweavers.com:8080/job/buttonmen-cgolubi1/371/

Sorry it took me so long to actually issue a pull for this; i've had it sitting around for ages.  I think i was hampered by the lack of a buttonmen-jenkins branch, but i'm not sure why...  Anyway, we have all that now, so here goes.