Bug fixes and compiler warnings. Unix readline support, pass 1

Fix various compiler warnings.

Fix bug causing double free when a file isn't found.

Fix bug using uninitialized variable parsing null filename.

Fix bug causing crash when format 3 retrieval pointer encountered.

Add support for readline (command line editing and history on Unix)

Untangle NT I/O so it builds without the direct access SCSI API & works.

Report errors as text messages everywhere.

Add MSVC project files.

Implement most of dir/full

Partially implement XABITM

Add help to command tables.

Allow choice of VMS qualifiers or Unix options.
  mount /write // /dev/cdrom
or
  mount -write /dev/cdrom

Parse quoted strings as command parameters.
   Mount /write "/dev/cdrom"
   search [*...]*.txt "My words for you"

Resolve command, parameter & qualifier ambiguity from tables.

Consolidate the various makefiles into a common file with very small
platform-specific wrappers.  This simplifies maintenance.

Add diskio module to allow easy access to .iso images and simulator files.
Removes requirement for loop device or equivalent.  Builds as a separate
executable.

Writes to the ODS2 volumes are broken.

extracters/ods2/sysmsg.h

@@ -0,0 +1,6 @@
+#ifndef SYSMSG_H
+#define SYSMSG_H
+
+const char *getmsg( unsigned int vmscode );
+
+#endif