Fixed IndexOutOfBounds error associated with tail merging.

Don't expand out source nodes for tail merging, since that's a head merging action only.
This shows up as a bug only because we now allow merging tails against non-reference paths.
Update pom versions for the 3.2 release
Merge branch 'master' of https://github.com/broadgsa/gatk
v3.2-2-framework: Correctly recognize -XX java options to control GC memory usage.