added quick_and_dirty (from Isar/skip_proofs.ML);

--- a/src/Pure/ROOT.ML	Sat Sep 17 19:12:58 2005 +0200
+++ b/src/Pure/ROOT.ML	Sat Sep 17 19:17:33 2005 +0200
@@ -7,6 +7,8 @@
 val banner = "Pure Isabelle";
 val version = "Isabelle repository version";    (*filled in automatically!*)
 
+(*if true then some tools will OMIT some proofs*)
+val quick_and_dirty = ref false;
 
 print_depth 10;