Reworking to fit new FS interface.
Reworking to fit new FS interface.

(open_txn_root_args): Replace dir_p with root_p, an svn_fs_root_t.
(txn_body_open_txn_root): Adjust for this change.
(svn_fs_open_txn_root): Likewise.

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