Update the docs for the config file format.
Update the docs for the config file format.

* subversion/libsvn_subr/config_file.c (svn_config_ensure): Turn on the part
  of README.txt that talks about variable expansion, and note where the
  config files reside on Windows.

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