Introduce a new handbook-specific knob ``WITH_PGPKEYS'' and add the
relevant functions to the DSSSL stylesheet.

The default behavior is for print output formats to just display PGP
fingerprints unless you use `make WITH_PGPKEYS=1 FORMATS=ps'. This new
default behavior reduces the size of Appendix E from 52 pages to 9
pages, and that could be trimmed down more with a more efficient
layout for the fingerprints (does each entry really warrant a new
section header?)

Knob requested by: Chris Costello
Discussed on: -doc