Fix a Perl-to-APR conversion function.

* subversion/bindings/swig/perl/libsvn_swig_perl/swigutil_pl.c
  (svn_swig_pl_to_hash): This function is the universal converter
  from "Perl hash of some values" to "APR hash of (converted) values".
  It uses hv_iternextsv(H, &KEY, &LEN) to retrieve a Perl 
  hash key. This does _not_ copy the key string, but simply sets KEY
  to a pointer into Perl internal memory. svn_hash_sets() also does _not_
  copy KEY, so the returned apt_hash_t now contains a pointer into Perl memory.
  If Perl later garbage collects this memory this apt_hash_t key will point
  to random bytes and apr_hash_get() for this key will fail.
  Hence make a copy of the string and use that for svn_hash_sets().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1507044 13f79535-47bb-0310-9956-ffa450edef68