Make extended commands return defined flags

Instead of returning 0 or 1, we'll now use ECMD_OK or ECMD_TURN.
These have the same meaning as the hardcoded numbers; ECMD_TURN
means the command uses a turn.

In future, could add eg. a flag denoting "user cancelled command"
or "command failed", and should clear eg. the cmdq.

Mostly this was simply replacing return values with the defines
in the extended commands, so hopefully I didn't break anything.

include/hack.h

@@ -537,6 +537,10 @@ enum bodypart_types {
 #define BRK_KNOWN2NOTBREAK 8
 #define BRK_KNOWN_OUTCOME  (BRK_KNOWN2BREAK | BRK_KNOWN2NOTBREAK)
 
+/* extended command return values */
+#define ECMD_OK   0x00  /* cmd done successfully */
+#define ECMD_TIME 0x01  /* cmd took time, uses up a turn */
+
 /* values returned from getobj() callback functions */
 enum getobj_callback_returns {
     /* generally invalid - can't be used for this purpose. will give a "silly