read_properties: use size_t instead of int for callback

[tig] / TODO

TODO
----
Features that should be explored.

 - Repository status view.

 - Add interface (somewhat like git-gui has) allowing a diff chunk to be
   staged/unstaged for the next commit.

 - Better text-input support. From setsyx(3):

	The setsyx routine sets the virtual screen cursor to y, x.  If y and x
	are both -1, then leaveok is set.  The two routines getsyx and setsyx
	are designed  to  be used by a library routine, which manipulates
	curses windows but does not want to change the current position of the
	program cursor.  The library routine would call getsyx at the
	beginning, do its manipulation of its own windows, do a wnoutrefresh on
	its windows, call  setsyx,  and then call doupdate.

 - When the user wants to "view" a commit, you could show from which branch
   heads and from which tags the commit is reachable, and perhaps which tag is
   the latest among the ones reachable from that commit, as part of the commit
   detail information you display on the lower pane (log/diff view).

 - Use autoconf to check for iconv in libc and how it is declared (the
   2nd argument is 'const' on FreeBSD / Mac OS X). Maybe also check for
   the AsciiDoc and XmlTo document tools.

 - The autoconf check could also be used to determine whether it is a
   newer git so that git-config will be used instead of git-repo-config.