in polCalc_FITS(): Included the ability to mask maps based on sigma_QU as well as sigma_I
Edited print statements.
I now first run polCalc_FITS to mask everything in the pct maps below 3.5 sigma.  Also changed the grayscale stretch from linear to log.
Change IRAS4B/4A values from 100 to 999, to indicate that there aren't good Stokes I values.
Tweaked plot and print statements.
Corrected scaling of bolo segtors: now they're *actually* scaled by pol intensity, not by total intensity.