recognize dock windows (and support matching them)

include/data.h

@@ -228,6 +228,9 @@ struct Window {
 
     /** Whether the application used _NET_WM_NAME */
     bool uses_net_wm_name;
+
+    /** Whether the window says it is a dock window */
+    bool dock;
 };
 
 struct Match {
@@ -239,6 +242,7 @@ struct Match {
     char *class;
     char *instance;
     char *mark;
+    int dock;
     xcb_window_t id;
     Con *con_id;
     enum { M_ANY = 0, M_TILING, M_FLOATING } floating;

include/match.h

@@ -1,6 +1,14 @@
 #ifndef _MATCH_H
 #define _MATCH_H
 
+/*
+ * Initializes the Match data structure. This function is necessary because the
+ * members representing boolean values (like dock) need to be initialized with
+ * -1 instead of 0.
+ *
+ */
+void match_init(Match *match);
+
 /**
  * Check if a match is empty. This is necessary while parsing commands to see
  * whether the user specified a match at all.