Makes the script stops on failures, fixes usage string
Limits output of 'git show'

It was waiting for user input on my system (the pager was triggered).
Correctly set LOCAL_M2_REPO using BASEDIR
Automatically add pr pull location for Scala

And do check out the requested Scala commit.
Checks that the right version of Java is used
Sets the ANT_OPTS needed for a clean Scala build
Made JAVA check optional.
Merge remote-tracking branch 'origin/add-options'

Conflicts:
	validator.sh
Tweaks for post-modularization sbinary (hardcodes scalaBinaryVersion)
Fixes #4