[GSOC] Have the testsuite built when the 'check' target is invoked.

[GSOC] Have the testsuite built when the 'check' target is invoked.
Support a separate target named 'testsuite' which builds the test suite
without running it.

Also note that a configure option (--enable-gtest) must explicitely
be set in order to configure the Google Test Framework. If it is
not set, running the 'check,' 'testsuite,' or 'testframework,'
make targets will simply display a message saying the framework
has not been configured.