Don't use XRANDR 1.3 extensions if the server doesn't support them.

Don't use XRANDR 1.3 extensions if the server doesn't support them.

* src/xterm.h (struct x_display_info): Add fields to save XRANDR
version number.
* src/xfns.c (x_get_monitor_attributes): Save the version numbers
after querying the X server.
(x_get_monitor_attributes_xrandr): Don't use XRRGetOutputPrimary or
XRRGetScreenResourcesCurrent if the server doesn't support at least
RANDR version 1.3.  Conditionalize the code blocks on compiling
against library version 1.3 or better, rather than feature tests for
each function.
* configure.ac: Stop testing for those two functions.