Replace Test::More with t/test.pl in DynaLoader.t.

Test::More has dependencies on dynamically loaded modules and thus
isn't appropriate for running a basic test of whether dynamic
loading is working.  Plus it provides no features we're using
that aren't also in t/test.pl.  (Just had to make the second
argument to like() a regex instead of a string.)
Bump POSIX version following a7ea4c68ecf.
Bump XSLoader version after 4821216b2814.