PDF: Allow per-unit default parameters

Allow units to provide default PDF parameters for ATTACH, e.g. columns should match physical device.

Allow image="" to mean "no image" so a default can be replaced with "no image"

Also default NULL UNIT pointers in help routines to unit 0 - SCP passes NULL in some circumstances.

Correct conditional help topic compilation.
NOVA: Upgrade lpt to sim_pdflpt
H316: Upgrade lpt to sim_pdflpt
HP2100: Upgrade lpt to sim_pdflpt
I1401: Upgrade lpt to sim_pdflpt
I1620: Upgrade lpt to sim_pdflpt
I7094: Upgrade lpt to sim_pdflpt
PDF: Support attaching to stdout

Non-pdf only.

Reserved filename '-'

Note that it must be seekable.
IBM1130: Upgrade lpt to sim_pdflpt
Interdata: Upgrade lpt to sim_pdflpt
PDP-1: Upgrade lpt to sim_pdflpt
PDP-8: Upgrade lpt to sim_pdflpt
S3: Upgrade lpt to sim_pdflpt
SDS: Upgrade lpt to sim_pdflpt
PDP-18B: Upgrade lpt to sim_pdflpt
PDF: Update detach checks

Now that pdflpt manages non-pdf output, the detach validity checks need to move up.
PDF: Fixes to build under VS2008
PDF: Update VS project files

This updates the VS project files to build with the PDF libraries.

It also adds two small projects to the build:
  lpt2pdf - a stand-alone utility for converting ASCII files to PDF
  PDFWatcher - a sample, unsupported spooled directory watcher for Windows.

lpt2pdf is also in the makefile.  PDFWatcher, since it's Windows Only, is not.
PDF: Remove <stdint.h> from lpt2pdf.h

Not needed for using the API
PDF: Less ugly VS2008 typedefs

Only slightly less ugly.