Man page improvements for discussd and disserve

- Incorporate changes from Alex Dehnert to clarify
  the purpose of disserve and discussd, and also correct
  typos.
Make dsmail always retain default fields

- dsmail should retain the default fields, as disk is cheap
  (Trac: #1114)
- Add -x option to _not_ retain default fields
- Change the -A, -d, and -D options to not be toggles if
  specified multiple times.
Add a VERSION file and release 10.0.17