explicit specify to not support WIDE=Y for DOS port

* raise error by the preprocessor in the port specific include file
* note in README pointing to DOSVGA port

fixes #290 (by explicit and documented "break")

dos/README.md

@@ -18,6 +18,8 @@ Building
   Watcom, specifying "MODEL=f" (flat) will automatically switch to a
   32-bit build.
 
+  Note: if you want WIDE support use the DOSVGA port instead.
+
 - Optionally, you can build in a different directory than the platform
   directory by setting PDCURSES_SRCDIR to point to the directory where
   you unpacked PDCurses, and changing to your target directory:

dos/pdcdos.h

@@ -1,6 +1,11 @@
 /* PDCurses */
 
 #include <curspriv.h>
+
+#if defined( PDC_WIDE)
+   #error DOS port has no WIDE support
+#endif
+
 #include <string.h>
 
 /*----------------------------------------------------------------------