Substantial improvements on several fronts, mostly to do with

extraction:  Fixed a problem causing long extraction times, at
least some of which had to do with a poor string hash function
implementation.  Fixed a huge problem in ext2spice, where the
node merge function was particularly poorly implemented, causing
exponentially increasing processing times with layout size.
Corrected a minor issue with ext2spice where arguments were
improperly specified, causing unnecessary error messages to be
issued.  Fixed an error in the "load -dereference" command option,
which again caused unnecessary error messages to be issued.
Changed .gitignore to ignore Depend files, which are now regenerated
on every build.

extract/ExtSubtree.c

@@ -145,6 +145,7 @@ extSubtree(parentUse, reg, f)
     bool result;
     int cuts, totcuts;
     float pdone, plast;
+    SearchContext scx;
 
     if ((ExtOptions & (EXT_DOCOUPLING|EXT_DOADJUST))
 		   != (EXT_DOCOUPLING|EXT_DOADJUST))
@@ -231,9 +232,8 @@ extSubtree(parentUse, reg, f)
 	    {
 		/* Make sure substrate connections have been handled	*/
 		/* even if there were no other interactions found.	*/
-		SearchContext scx;
 
-		GEOCLIP(&ha.ha_clipArea, &r);
+		ha.ha_clipArea = r;
 		scx.scx_trans = GeoIdentityTransform;
 		scx.scx_area = r;
 		scx.scx_use = ha.ha_parentUse;