Users can control if usual log severity values will be defined by
GLOG_NO_ABBREVIATED_SEVERITIES.

For http://code.google.com/p/google-glog/issues/detail?id=105



git-svn-id: https://google-glog.googlecode.com/svn/trunk@101 eb4d4688-79bd-11dd-afb4-1d65580434c0