Have newcham() give messages when monsters polymorph in more cases

This is a descendent of an earlier patch I wrote. The main idea is still
to clearly communicate to the player *what* something is turning into,
without the need to farlook afterwards, and give them the opportunity to
add MSGTYPE for when something jumps on a polymorph trap and becomes an
arch-lich. If it happens out of sight, the player also might get a whiff
of the monster's smell, giving a bit of advance warning.

There is one new case in here, in normal_shape(), which came about
because I noticed a weird message sequence: "The magic-absorbing blade
cancels the python!  You kill the chameleon!" with no intervening
message indicating the python reverted to a chameleon.

src/mon.c

@@ -3808,7 +3808,7 @@ normal_shape(struct monst *mon)
     if (mcham >= LOW_PM) {
         unsigned mcan = mon->mcan;
 
-        (void) newcham(mon, &mons[mcham], FALSE, FALSE);
+        (void) newcham(mon, &mons[mcham], FALSE, TRUE);
         mon->cham = NON_PM;
         /* newcham() may uncancel a polymorphing monster; override that */
         if (mcan)