fix github issue #1046 - tutorial anomalies

Reported by Noisytoot:  going from level tut-1 to tut-2 returned the
hero's starting equipment too soon, and exiting the tutorial from
tut-2 let the hero keep any equipment acquired within the tutorial.

Entering and leaving the tutorial was being handled by lua code in
the level description of tut-1 and adding a second level messed that
up.  I didn't see any way of handing that with level-specific lua
code so I made it become the core's responsibility.  gotolevel()
knows when the hero is moving from one dungeon branch to another so
it can recognize entry to or exit from the tutorial easily.

While fixing this, prevent #invoke of the Eye of the Aethiopica from
offering the tutorial as a candidate destination (was feasible if it
had been entered at start of game).

Not fixed:  levels visited in the tutorial become part of #overview.

Show location as "Tutorial:1" instead of "Dlvl:1" on status lines.
Only tested with tty; some interfaces handle location themselves and
may need their own fixup for this.

Fixes #1046

doc/fixes3-7-0.txt

@@ -1604,6 +1604,11 @@ running the tutorial until completion and returning to normal play but left
 when a magic whistle moved a hidden pet it brought that out of hiding and
 	gave a message about "your <pet> appears" but the map was updated
 	while it was still hidden so nothing seemed to appear
+entering the tutorial stashed hero's equipment for eventual return to normal
+	play but going down stairs to the second tutorial level returned it
+	too soon and allowed any items gathered on the first level to be kept
+entering the tutorial and then returning to play made the tutorial branch be
+	eligible for a portal destination via wizard's Eye of the Aethiopica
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository