smurf: sc2ast: added flips for FTS-2 daisies.

First attempt at reducing daisy scans while FTS-2 is in the beam.
smurf: sc2ast: use SMURF_FTS_PORT for flips.

Now only applies FTS-2 port flips if this environment variable
is set.  Uses the variable to determine which port was pointed
at the source.

Moved variable declarations to the top of the function, and
re-used the AST mapping pointers.
smurf: Added skeleton fts2filtermap command.

Currently the filtering is not implemented.
smurf: Rename fts2filtermap to fts2maskmap

This is to avoid confusion with the unrelated
sc2filtermap program.
smurf: fts2maskmap now masks by offset position

Row and column numbers are transformed to offsets in the
moving coordinate frame and used to determine which
pixels to filter.
smurf: Improved performance of fts2maskmap

Provided tolerance information to astTranGrid and only
re-generate the coordinate conversions every few steps.
smurf: Also use FTS-2 port area in fts2maskmap

An additional masking check now limits the pixels to those
within the FTS-2 port area.