[Reviewer: Matt] Add a check for any memory errors 

Matt, can you please review this change to the makefile to output to screen when there are valgrind errors when running the UTs

The output will look like:

Error: some memory errors have been detected
Leak_DefinitelyLost
See /home/em/sprout/build/testout/vg_sprout_test.memcheck for further details.

Fixes #264