make update-pot will not touch pot file if msgid's are unmodified
    
    Formerly running 'make update-pot' would write an insignificantly
    different pot file even if the msgid's xgettext found were unmodfied.
    Now the result of running xgettext is compared to the existing
    pot file after adjusting for things like timestamps, and only
    copies the result of xgettext to the new pot file if there
    were differences.
    
    This will help eliminate git commits on the pot file if all one
    did was see if the pot file was up to date, if it was up to date
    git won't see any modifications. It used to be that timestamps
    would be different in the pot file just by virtue of checking
    if the pot file was current.
    
    fix exit status; replace POT with $(DOMAN).pot