Add xrdp-waitforx to wait for X to start with RandR outputs

For some window managers (fvwm2 and fvwm3) if the X server isn't
running and has output it's possible for the window manager to fail or
reconfigure randr incorrectly.

With xrdp-waitfox:
 - Install xrdp-waitfox to the BIN dir.
 - sesman will run xrdp-waitfox as the logged in user.
 - Set an alarm to exit after 30 seconds.
 - Try to open env DISPLAY value's display (10 seconds).
 - Test for RandR extension.
 - Wait for outputs to appear (10 seconds).

waitforx/Makefile.am

@@ -0,0 +1,10 @@
+bin_PROGRAMS = \
+  xrdp-waitforx
+
+AM_LDFLAGS = -lX11 -lXrandr
+AM_CFLAGS = -I$(top_srcdir)/common
+
+xrdp_waitforx_SOURCES = waitforx.c
+
+xrdp_waitforx_LDADD = \
+  $(top_builddir)/common/libcommon.la