gjs-unit: Allow running just one test case
gjs-unit: Allow running just one test case

For example:
$ env TOP_SRCDIR=. BUILDDIR=. GI_TYPELIB_PATH=. G_SLICE=always-malloc libtool --mode=execute valgrind --leak-check=full --suppressions=test/gjs.supp --log-file=/tmp/gjs-valgrind.log  ./gjs-unit testGIMarshalling.js

magcius/gjs,endlessm/gjs,djdeath/gjs,magcius/gjs,endlessm/gjs,djdeath/gjs,djdeath/gjs,mtwebster/cjs,mtwebster/cjs,mtwebster/cjs,endlessm/gjs,pixunil/cjs,mtwebster/cjs,magcius/gjs,endlessm/gjs,pixunil/cjs,djdeath/gjs,pixunil/cjs,djdeath/gjs,mtwebster/cjs,pixunil/cjs,magcius/gjs,pixunil/cjs,endlessm/gjs,magcius/gjs