curses follow-up bits

Move the curses global variable defininitions to cursmain.c.

Make the references to those global variables extern in
include/wincurs.h

Get rid of a warning:
../win/curses/cursmesg.c:379:9: warning: declaration shadows a
variable in the global scope [-Wshadow] int orig_cursor = curs_set(0);

Kludge for Visual Studio compiler: Add a stub- file for use
in Windows curses port builds to ensure that a needed #pragma
is invoked prior to compiling the file pdcscrn.c in the
PDCurses source distribution. All command line options and
compile of the file. It is unreasonable to expect a NetHack
builder to have to tinker with the PDCurses source files in
order to build NetHack. This kludge means the NetHack builder
doesn't have to.
The file stub-pdcscrn.c contains only two lines:
	#pragma warning(disable : 4996)
	#include "pdcscrn.c"
Some day, if the PDCurses sources corrects the issue, this
can go away.

win/curses/cursmain.c

@@ -80,6 +80,16 @@ struct window_procs curses_procs = {
     genl_can_suspend_yes,
 };
 
+/*
+ * Global variables for curses interface
+ */
+ 
+int term_rows, term_cols;   /* size of underlying terminal */
+int orig_cursor;	    /* Preserve initial cursor state */
+WINDOW *base_term;          /* underlying terminal window */
+boolean counting;           /* Count window is active */
+WINDOW *mapwin, *statuswin, *messagewin;    /* Main windows */
+
 /* Track if we're performing an update to the permanent window.
    Needed since we aren't using the normal menu functions to handle
    the inventory window. */