[daip] FLATN enhancement

[Rob Ivison]

dear Eric et al.

i'll confess before i start that i haven't thought through how complex 
this task might be, or whether a combination of other tasks could 
accomplish it, but i know that several groups have been battling with 
methods of correcting for bandwidth smearing in their analysis of 
stacked data and this would help.

would it be possible to add another option "BWSM" to OPTYPE in FLATN 
(alongside NOIS and WEIG) that would enable the user to generate an 
image of "bandwidth smearing" (of the kind reported by JMFIT).

ideally, this would generate an image of correction factors, using the 
distance from the pointing centre, the synthesized beamsize (from the 
image header) and a fractional bandwidth taken from... aparm(10)?

an enhancement would be to add a "BWPA" option which would yield an 
image wherein each pixel contained the PA of the smearing.

i have written some IDL code to calculate the correction but it's 
clunky and it'd be better/safer if everyone was using the same code.

doing a version of "BWSM" that worked with multiple pointings should 
be possible (since NOIS and WEIG work for multiple pointings), but 
"BWPA" wouldn't make much sense. people would have to run "BWPA" for 
individual pointings to deal with multiple smearing directions.

cheers,

Rob