level teleporters vs Ft.Ludios

From newsgroup discussion where slash'em changes have revealed a
latent nethack bug:  prevent placing level teleporters in single-
level branches.  The Knox level doesn't have any level teleporters
(or random traps) but wizard mode wishing could create them there.
They wouldn't do anything because the only possible destination
would be the same level.  Pushing a boulder onto one used to trigger
an infinite loop (and still does in slash'em, which has other
single-level branches besides Ft.Ludios) trying to relocate it.

Boulder pushing was changed 15 years ago to prevent the infinite
loop and to avoid giving "the boulder disappears" message when a
level teleporter failed, but rolling boulder traversal lacked that
same change--it wasn't vulnerable to looping but could give an
inaccurate message claiming that the boulder disappeared when it
actually didn't.  Fixing this is a bit late; rolling boulder trap
creation was recently changed to not choose a path that rolls over
teleportation or level tele traps any more.

doc/fixes37.0

@@ -449,6 +449,9 @@ turn off input autocompletion for '#twoweapon' since simple 'X' invokes it;
 	likewise for #wizdetect (^E), #wizgenesis (^G), #wizidentify (^I),
 	#wizlevelport (^V), #wizmap (^F), and #wizwish (^W); probably ought
 	to do so for #overview (^O) too but that one still autocompletes
+if a branch has only one level (Fort Ludios), prevent creation of any level
+	teleporters there (level definition doesn't have any but wizard mode
+	wishing could attempt to place one)
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository