Remove SIGPOLL usage (#385)

* Remove unnecessary calls to XLOCK/XUNLOCK

The X methods called by flush_display_region() and flush_display_lineregion() handle the
locking/unlocking, therefore it is unnecessary to invoke the locking here.

* Remove explict signals when doing XUNLOCK()

Call getXsignaldata() directly if a signal happened while X code
was locked, instead of generating a signal and then handling it.

Some macros and functions needed to pass the DspInterface instead of
extracting the X display and window and passing those so that the
correct structure was available for the XUNLOCK() call.

src/initkbd.c

@@ -411,7 +411,7 @@ static u_char *make_X_keymap() {
   XDisplayKeycodes(currentdsp->display_id, &minkey, &maxkey);
   codecount = maxkey + 1 - minkey;
   mapping = XGetKeyboardMapping(currentdsp->display_id, minkey, codecount, &symspercode);
-  XUNLOCK;
+  XUNLOCK(currentdsp);
 
   for (; *key_sym_pairs != -1;) {
     int reusable = *key_sym_pairs++, code = *key_sym_pairs++, sym = *key_sym_pairs++, xcode;