make mask file report object number

[MatthewWhiting]

Request from Cormac Purcell:

I have one Duchamp request which might be simple enough to implement 
quickly. Would it be possible to output a mask file with the pixels
set to the clump number rather than a value of one?

Should be easy to implement. May want to keep the option of just having values of 1 for detected pixels, so might introduce another flag (flagMaskWithObjectNum or something...) so that the user can select which format of mask.

[MatthewWhiting]

Done and is working. Committed in [521].

I've also added code to change the BUNIT keyword in the MASK fits file, so that it records either "Detection Flag" or "Object ID" accoring to the flagMaskWithObjectNum value.

Feature will be available in next release, which will hopefully be very soon.

Closing ticket.