Follow-up to r1397846.  Fix check-swig-rb to run properly on OS X.

Too much copy and paste and not enough real thought. :(

* Makefile.in
  (TEST_SHLIB_VAR_SWIG_RB): Use the SWIG_RB paths not SWIG_PY and ruby
    uses libsvn_swig_ruby instead of libsvn_swig_rb.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1535161 13f79535-47bb-0310-9956-ffa450edef68