Update a comment to match r875303 changes.

* subversion/include/svn_types.h: Update the overview comment about
  special files to use the new function name in libsvn_subr/subst.c.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1751399 13f79535-47bb-0310-9956-ffa450edef68
1 file changed