Log Message:
Update to version 9.20, including security fix.

Changes:
- (libptytty) fix bug that prevented urxvtd from writing utmp
  entries when using --fork (reported by Ryan Kavanagh).
- security bugfix: window property values could be queried even
  in secure mode (reported by Phillip Hallam-Baker).
- fix build when perl is enabled and fading is disabled.
- fix regression that broke continuous scrolling when pressing
  and holding the scrollbar up or down button, gentoo bug #493992.
- increase the maximum length of a command sequence to 32k bytes,
  to allow longer OSC sequences (previous limit was 2k).
- new Ctrl-Meta-c and Ctrl-Meta-v bindings to interact with
  the CLIPBOARD selection.
- new extension: selection-to-clipboard.
- the extensions macosx-clipboard and macosx-clipboard-native
  are deprecated and will be removed in the next release.
  Support for the clipboard on OS X can be more generally
  enabled by setting the XQuartz preference to sync the OS X
  pasteboard and the X11 clipboard.