created testing harness for immutability checker. fixed bug related to comparing heap locations to null -- path constraints were not being eliminated
this test has been renamed
Merge branch 'master' of https://github.com/sblackshear/thresher

Conflicts:
	src/edu/colorado/thresher/Main.java
Merge branch 'master' of https://github.com/sblackshear/thresher
adding immutability tests
adding support for new tests