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/worm.c

@@ -377,7 +377,7 @@ cutworm(worm, x, y, weap)
     /* Create the second worm. */
     new_worm  = newmonst(0);
     *new_worm = *worm;			/* make a copy of the old worm */
-    new_worm->m_id = flags.ident++;	/* make sure it has a unique id */
+    new_worm->m_id = context.ident++;	/* make sure it has a unique id */
     new_worm->wormno = new_wnum;	/* affix new worm number */
 
     if (worm->mtame)