More isometric display checked in

[Stan Shebs]

Continuing my quixotic quest to avoid quashing quirks and bugs,
I've checked in a bunch more isometric support in the tcl/tk interface.
The basic drawing algorithm no longer tries to draw the whole world,
view rotation works sensibly, and connection terrain is drawn.

To use it, just click on the left-side buttons that are now enabled,
or '@' to toggle.  To see vertical exaggeration, you need to use a
prefix to the '@' command, so '5' '@' increases vertical scaling
by a factor of five.

Movement and display of units is still squirrelly, only solid-color
terrain is available, borders and other decor are missing, so at
the moment it's more useful to help visualize terrain (such as for
panzer) than for actual play.

Stan