Global changes

• The NAG library is no longer used, and thus KAPPA is available via the Starlink Software Store.

• Standardized the implementation status in the reference section, and corrected the HISTORY processing.

• Improved the documentation: clarified and reduced the usage of the term `magic pixel'; added more warnings about metacharacters in C-shell usage; updated the related applications; extended the FITS airlock to include the new editing commands; added a new section on bad-pixel removal; and corrected various typographical errors, mostly in the reference section.

• The reference dataset in the AGI database  may be a foreign file and/or include an NDF section.

• Several tasks use a faster method of managing workspace.