'$' vs #jump

'$' vs #jump

Hero poly'd into xorn can wear jumping boots or cast jump spell, so
some target destinations which were excluded by '$' (to show valid
destinations during getpos) shouldn't have been.  Doubly so if
wearing the Eyes of the Overworld where xorn'd hero can jump through
walls rather than just into them.

This attempts to deal with diagonal moves vs open doorways sanely,
including allowing knight's move jumps in or out of them when
appropriate.

Also, need to check isok(x,y) before cansee(x,y) instead of after.