Fix xcb error ignoring

The existing mechanism with set_ignore_next() is (IMHO) ugly and also
does not work with XCB requests. This commit adds a new function
set_ignore_cookie() and fixes callers that were converted to XCB to use
this new function instead.

Signed-off-by: Uli Schlachter <psychon@znc.in>

src/common.h

@@ -1995,6 +1995,14 @@ set_ignore_next(session_t *ps) {
   set_ignore(ps, NextRequest(ps->dpy));
 }
 
+/**
+ * Ignore X errors caused by given X request.
+ */
+static inline void
+set_ignore_cookie(session_t *ps, xcb_void_cookie_t cookie) {
+  set_ignore(ps, cookie.sequence);
+}
+
 /**
  * Check if a window is a fullscreen window.
  *