Log Message:
Update to 318:

Patch #318 - 2015/04/12

* rename new(er) configure option --enable-initial-erase to
  --enable-pty-erase, since that conflicted with an existing option
  (report by Jens Schweikhardt).
* fix cut/paste error in --with-builtin-xpms configure option
  (reports by Jens Schweikhardt, Ross Combs).
* fix minor formatting issue in xterm manual (report by Jens
  Schweikhardt).
* eliminate unnecessary "#(vi" markers in autoconf macros by using
  "(" to begin case-statement cases (suggested by Jens Schweikhardt).
* minor fixes to improve const usage (Ross Combs).