Need Ruby expertise to fix SvnClientTest::test_cleanup

Recently, I tweaked the bindings so that the APR status and error codes
were wrapped. As a side effect, that allowed the
SVN_ERR_*_CATEGORY_START macros to be wrapped by SWIG.

As a side effect of *that*, the Ruby bindings now have a bug:

When a svn_error_t whose constant happens to be the first in its
category (i.e., its apr_err equals one of the CATEGORY_START constants),
Ruby thinks it has a FOO_CATEGORY_START error, not whatever the real
error is.

This is causing SvnClientTest::test_cleanup to fail.

Someone needs to fix the "Ext::Core.constants.each do |const_name|" loop
in svn/error.rb to ignore constants ending with _CATEGORY_START. Since I
do not know any Ruby, that someone cannot be me.

Max.