Fix incorrect expansion/replacement of the LIBTOOL_M4 and LIBTOOL_CONFIG
environment variables in autogen.sh.

* autogen.sh (ltfile, configfile): The file basename we're searching for
  must not be part of the replacement expansion when LIBTOOL_M4 or
  LIBTOOL_CONFIG are not defined.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1637826 13f79535-47bb-0310-9956-ffa450edef68