Extend --add-location option to suppress line number output

Extend --add-location option to suppress line number output

The --add-location option of msgattrib, msgcat, msgcomm, msgconv,
msgen, msgfilter, msggrep, msgmerge, msguniq, and xgettext
commands now takes an optional argument 'never', 'full', or
'file', to control the format of "#: ..."  comments.

The default catalog reader changed to always remember file
positions so the line number part can be suppressed in output
phase rather than input phase.