SRE fixes for 2.1 alpha:

-- added some more docstrings
-- fixed typo in scanner class (#125531)
-- the multiline flag (?m) should't affect the \Z operator (#127259)
-- fixed non-greedy backtracking bug (#123769, #127259)
-- added sre.DEBUG flag (currently dumps the parsed pattern structure)
-- fixed a couple of glitches in groupdict (the #126587 memory leak
   had already been fixed by AMK)
diff --git a/Modules/sre_constants.h b/Modules/sre_constants.h
index 5c55c3d..6cad089 100644
--- a/Modules/sre_constants.h
+++ b/Modules/sre_constants.h
@@ -6,7 +6,7 @@
  * NOTE: This file is generated by sre_constants.py.  If you need
  * to change anything in here, edit sre_constants.py and run it.
  *
- * Copyright (c) 1997-2000 by Secret Labs AB.  All rights reserved.
+ * Copyright (c) 1997-2001 by Secret Labs AB.  All rights reserved.
  *
  * See the _sre.c file for information on usage and redistribution.
  */
@@ -42,10 +42,12 @@
 #define SRE_OP_SUBPATTERN 28
 #define SRE_AT_BEGINNING 0
 #define SRE_AT_BEGINNING_LINE 1
-#define SRE_AT_BOUNDARY 2
-#define SRE_AT_NON_BOUNDARY 3
-#define SRE_AT_END 4
-#define SRE_AT_END_LINE 5
+#define SRE_AT_BEGINNING_STRING 2
+#define SRE_AT_BOUNDARY 3
+#define SRE_AT_NON_BOUNDARY 4
+#define SRE_AT_END 5
+#define SRE_AT_END_LINE 6
+#define SRE_AT_END_STRING 7
 #define SRE_CATEGORY_DIGIT 0
 #define SRE_CATEGORY_NOT_DIGIT 1
 #define SRE_CATEGORY_SPACE 2