* Makefile.in: Add new target for single-file User's Guide, use new
cygwin.dsl for output.
* cygwin.dsl: New file, DSSSL stylesheet for custom Cygwin output.
* cygwin-api.in.sgml: Update to DocBook SGML 4.2 DTD.
* cygwin-ug-net.in.sgml: Update to DocBook SGML 4.2 DTD.
* cygwin-ug.in.sgml: Update to DocBook SGML 4.2 DTD.
* cygwinenv.sgml: Correct some tags. Add description of default values
to ntsec, export, and error_start items.
* dll.sgml: Add explanation of cyg prefix for DLLs.
* effectively.sgml: Use systemitem tag for names of Cygwin packages.
* how-programming.texinfo: Add example to FAQ entry.
* pathnames.sgml: Add discussion of /proc filesystem.
* setup-net.sgml: Correct some typos and grammar.
