devdraw, acme, snarfer: remove 64KB snarf buffer limit

The snarf code silently dropped text larger than SnarfSize (64KB),
causing paste to produce nothing. Replace the static clip buffer
with a dynamically allocated one, remove all the size checks, and
read the actual X11 property size instead of capping at SnarfSize.

include/draw.h

@@ -547,10 +547,6 @@ extern	void		drawsetdebug(int);
 /*
  * Snarf buffer
  */
-enum
-{
-	SnarfSize = 64*1024
-};
 char *getsnarf(void);
 void putsnarf(char*);