tmux needs an older file on 10.4.11

[Jan Stary]

I am trying to build sysutils/tmux on MacOSX 10.4.11
It fails because 10.4.11 (Darwin 8.11.0) does not have
libproc.h that is included by tmux's osdep-darwin.c:

  osdep-darwin.c:22:21: error: libproc.h: No such file or directory

This problem has been encountered before,
and there is even a known workaround.
use an older version of osdep-darwin.c

http://sourceforge.net/mailarchive/forum.php?thread_name=51A035A8.6090504%40gmail.com&forum_name=tmux-users

I would like to prepare a diff to the tmux Portfile
so that it builds on my 10.4.11, but I am not sure
what is the right way to do this.

Does macports have the ability to say, in a Portfile,

  "if we are pre-10.5, replace osdep-darwin.c with
  git checkout c1b994852594b23b7443e01e05257c991684ba4e -- osdep-darwin.c" ?

Or would it be better to just hold a copy of that version of the file
in the port's files/, and conditionally use it on pre-10.5?

	Jan