engine: the one capability is a flag

Cclientpreedit was a one-bit mask that every producer set as "want ?
Cclientpreedit : 0" and every consumer masked out again; nothing else
was ever going to join it.  Keyreq carries clientpre, an int that says
whether the client draws the preedit, and the engine and the XIM
context keep it under that name.

dat.h

@@ -173,10 +173,6 @@ struct Popup
 typedef struct Keyreq Keyreq;
 typedef struct Keyres Keyres;
 enum
-{
-	Cclientpreedit	= 1<<0,
-};
-enum
 {
 	Keypress,
 	Keyreset,
@@ -186,7 +182,7 @@ enum
 };
 struct Keyres
 {
-	int	eaten;	/* Keycap: caller is active and capability was applied. */
+	int	eaten;	/* Keycap: the caller is the owner and clientpre took. */
 	Str	commit;
 	Str	preedit;
 };
@@ -194,7 +190,7 @@ struct Keyres
 struct Keyreq
 {
 	void	*owner;	/* stable until the context's release is acknowledged */
-	int	cap;
+	int	clientpre;	/* the client draws the preedit; the popup does not */
 	int	op;
 	u32int	ks;
 	u32int	mod;