trunk only: preserving context (src files)

Pat Rankin wrote:
> collect them all into some new struct and
> save that separately rather than jamming more non-option stuff
> into struct flags.

This patch:
- collects all context/tracking related fields from flags
  into a new structure called "context."
It also adds the following to the new structure:
- stethoscope turn support
- victual support
- tin support

src/display.c

@@ -1191,7 +1191,7 @@ docrt()
     /* overlay with monsters */
     see_monsters();
 
-    flags.botlx = 1;	/* force a redraw of the bottom line */
+    context.botlx = 1;	/* force a redraw of the bottom line */
 }
 
 
@@ -1327,7 +1327,7 @@ void
 cls()
 {
     display_nhwindow(WIN_MESSAGE, FALSE); /* flush messages */
-    flags.botlx = 1;		/* force update of botl window */
+    context.botlx = 1;		/* force update of botl window */
     clear_nhwindow(WIN_MAP);	/* clear physical screen */
 
     clear_glyph_buffer();	/* this is sort of an extra effort, but OK */
@@ -1362,7 +1362,7 @@ flush_screen(cursor_on_u)
     display_nhwindow(WIN_MAP, FALSE);
     reset_glyph_bbox();
     flushing = 0;
-    if(flags.botl || flags.botlx) bot();
+    if(context.botl || context.botlx) bot();
 }
 
 /* ========================================================================= */