- remove redundant range check for buttons in conf_bind_mouse.

- make conf_bind_kbd return error on non-matches to match what
   conf_bind_mouse does.
 - rename some variables while here for clarity.
 - constify bind and cmd.

from Tiago Cunha.

parse.y

@@ -155,7 +155,12 @@ main		: FONTNAME STRING		{
 			free($2);
 		}
 		| BIND STRING string		{
-			conf_bind_kbd(conf, $2, $3);
+			if (!conf_bind_kbd(conf, $2, $3)) {
+				yyerror("invalid bind: %s %s", $2, $3);
+				free($2);
+				free($3);
+				YYERROR;
+			}
 			free($2);
 			free($3);
 		}