Update makefile

I removed references to LIBMEMSIM and LIBCOMMSOCK from makefile since
these libraries were rolled into LIBPINKYSIM some time back.
Purge *.gcda files before code coverage run

Remove old .gcda files before starting a new code coverage run.
Previously it would accumulate counts across runs as long as the source
file wasn't recompiled.  Now each test run gets a clean set of results.
MemorySim now supports more than 2 regions

I fixed a bug in the region linked list manipulation code so that more
regions would be supported correctly.