use new TEST_MEMCMP() in stringutils-test.c
use new TEST_MEMCMP() in stringutils-test.c

instead of TEST_BOOL(memcmp(...), false).  The test now prints the
contents of the two memory regions if the test fails, making it easier
to troubleshoot problems.

rhansen/rpstir,rhansen/rpstir,rhansen/rpstir,rhansen/rpstir,rhansen/rpstir