Fixing Makefile bug where it couldn't find build.mk if MOOSE_DIR wasn't set
refs #3058
Merge pull request #3081 from permcody/makefile_fix

Fixing Makefile bug where it couldn't find build.mk if MOOSE_DIR wasn't ...
Merge commit 'efe0deb4e07c13531f7e4af95cb16c079eda15f3'