Fix a memory problem identified by valgrind.
Fix a memory problem identified by valgrind.

* subversion/libsvn_wc/wc_db_pdh.c
  (svn_wc__db_drop_root): Use key corresponding to hash iterator.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion