ipc: share one keysym and modifier mapping across frontends

The keysym-to-engine-key rule lived in ibus.c, xim/xim.c and gtk/main.c,
and the copies disagreed: GTK sent keypad digits as special keys while
IBus and XIM sent '1'..'9'. Modifiers were rebuilt bit by bit in two
places although Mmask already is the X core layout; only the virtual
Super bit (26) that GDK and IBus set needs folding. ipckey/ipcmod in
ipc.c serve the daemon, the module and the tests.

ipc.c

@@ -223,6 +223,31 @@ Bad:
 	return -1;
 }
 
+/*
+ * Engine key for an X keysym and its Unicode value: printable characters
+ * as themselves, the function keysyms 0xff00-0xffff as Kspec+offset.
+ */
+uint32_t
+ipckey(uint32_t sym, uint32_t unicode)
+{
+	if(unicode >= ' ' && unicode != 0x7f)
+		return unicode;
+	if(sym >= 0xff00 && sym <= 0xffff)
+		return Kspec + (sym - 0xff00);
+	return unicode;
+}
+
+uint32_t
+ipcmod(uint32_t state)
+{
+	uint32_t m;
+
+	m = state & Mmask;
+	if(state & Msupervirt)
+		m |= Msuper;
+	return m;
+}
+
 void
 ipcpackreq(unsigned char req[Ipcreqsz], int want, uint32_t mod,
 	uint32_t key)