Survex 1.0.21 released

[Olly Betts]

Download from the usual place:

http://www.survex.com/download.html

Chasm support works again, I've added support for backsights and ignored
legs in Compass survey data, fixed the missing MS Windows icons, and
made a few tweaks to cavern.

I have rebuilt the versions for RISC OS and MSDOS on 286 or earlier machines.

Here's the usual summary of changes in 1.0.21:

* cavern: when reading Compass DAT files, we now processes compass and clino
  backsights, and recognise the "X" flag which indicates a leg should be
  entirely ignored.  And we now report correct line number with errors in
  Compass .MAK files.

* cavern: if "*infer plumbs on", don't infer a plumb if the clino is
  +/- 90 degrees, but the backclino isn't (and vice versa).

* cavern: fixed 3dx output so it actually works with Chasm once more.

* cavern: don't allocate extra space needed for producing 3dx output for
  Chasm unless we're actually producing that output - saves about 8 bytes
  per station.

* cavern: removed slightly too keen sanity check which could misfire in very
  unusual circumstances.

* (MS Windows Version): all .ico files except 3d.ico have been missing since
  1.0.17 (or maybe 1.0.16) - fixed.  You wouldn't notice this if you installed
  over an previous version.

Cheers,
Olly