fix #H2591 - sitting while swallowed (trunk only)

From a bug report, sitting while
swallowed gave "you are sitting on air," and the intended message "there are
no seats in here" was never reached.  Move the latter so that it works, and
add a new one when you try to sit while a grabber is holding on to you.

     Also add theft vs donning fixes entry which was left out two days ago.

doc/fixes35.0

@@ -404,6 +404,11 @@ items conferring life drain resistance were affected by drain life spell
 'a'pply command could be used to recogniize undiscovered potions of oil
 fix replacing an existing bones file in wizard mode [load?y, unlink?n, die?y,
 	save?y, replace?y] for configurations using external file compression
+theft of worn armor with wear/unwear delay would interfere with completion of
+	wearing or unwearing some other armor which also imposed a delay
+	(disrupted wear attempt for +N helm of brilliance would result in loss
+	of N points of Int and Wis; gauntlets of dexterity had similar problem)
+#sit while swallowed would give the wrong message
 
 
 Platform- and/or Interface-Specific Fixes