make PhiNode.singleValue behave correctly for null values (in guard phis)
findbugs: bump version

--HG--
extra : rebase_source : 63ee1decca202cdacebfdebe5d28abdf83edddeb
findbugs: add lafo mirror

--HG--
extra : rebase_source : 1cc13179d4bee2de5d0f9597b003d1c68d6bbf58
findbugs: fix URLs in mx helper

--HG--
extra : rebase_source : 4b71e930107f5ad8cff636ad4caa461826bc22b5
added tests for type resolution