fix #H5245 - levitation boots message sequencing

Report was for
  You finish taking off your boots.
  You float gently to the altar.  [destination was a red herring]
  [take some action to run through moveloop() for next turn]
  Your movements are slowed slightly because of your load.

Having float_down() do the next encumbrance check instead of
waiting for moveloop() to do so was straightforward.  However,
while testing I noticed the reverse situation (not due to the fix
for the above) when putting on levitation boots
  Your movements are now unencumbered.
  You finish your dressing maneuver.
  You start to float in the air!

Having float_up() do the encumbrance check isn't adequate to fix
this, because it takes multiple turns to put on boots but the
properties they confer are enabled immediately, so moveloop() runs
while hero is already levitating even though the game hasn't told
the player about it yet.  Fix is a hack to defer the effect of
levitation on encumbrance until the boots are fully worn, which
might lead to strangeness somewhere.  It's also boot-specific so
will need to be updated if some other multi-turn armor that confers
levitation ever gets added.

doc/fixes36.1

@@ -374,6 +374,10 @@ automatic #overview annotation for quest summons wasn't shown if the quest
 	entry portal was on same level as bigroom or rogue level
 gaining or losing strength while wearing gauntlets of power could give
 	misleading message about already being as strong or weak as possible
+levitation vs encumbrance message sequencing issues:  putting on boots of
+	levitation reported reduction of encumbrance before finish-wearing
+	and float-up messages, taking off such boots didn't report increase
+	of encumbrance until player took another action
 
 
 Fixes to Post-3.6.0 Problems that Were Exposed Via git Repository