[PATCH21.4] fix bug in parsing ^ after shy group in regex

[Julian Bradfield]

^ was wrongly interpreted as literal when occurring at the start
of a shy group. Cause: regex.c:at_begline_loc_p() was not told about
shy groups.
Two tests added to tests/automated/regexp-tests.el.

Patch applies against 21.4.22. (Patch for 21.5 follows.)

--- src/regex.c-dist	2006-03-31 02:29:00.000000000 +0100
+++ src/regex.c	2011-12-11 18:47:22.000000000 +0000
@@ -3295,12 +3295,18 @@
 {
   re_char *prev = p - 2;
   re_bool prev_prev_backslash = prev > pattern && prev[-1] == '\\';
+  re_bool shy_open = prev-1 > pattern && prev[0] == ':'
+    && prev[-1] == '?' && prev[-2] == '(';
+  re_bool ppp_backslash = prev-2 > pattern && prev[-3] == '\\';
 
   return
        /* After a subexpression?  */
        (*prev == '(' && (syntax & RE_NO_BK_PARENS || prev_prev_backslash))
        /* After an alternative?  */
-    || (*prev == '|' && (syntax & RE_NO_BK_VBAR || prev_prev_backslash));
+    || (*prev == '|' && (syntax & RE_NO_BK_VBAR || prev_prev_backslash))
+       /* After a shy open? */
+    || (!(syntax & RE_NO_SHY_GROUPS) && shy_open 
+      && (syntax & RE_NO_BK_PARENS || ppp_backslash));
 }
 
 
--- tests/automated/regexp-tests.el-dist	2008-12-26 03:45:29.000000000 +0000
+++ tests/automated/regexp-tests.el	2011-12-11 19:20:46.000000000 +0000
@@ -447,11 +447,16 @@
   (Assert (progn (string-match "\\(a\\)" "a")  
 		 (string-match "\\(?:a\\)" "a")  
 		 (not (match-beginning 1))))
+
+  ;; ^ at beginning of shy group. Fix by
+  ;; Julian Bradfield on 2012-12-11.
+  (Assert (string-match "\\(?:^\\)" ""))
+  (Assert (string-match "a(?:^)" "a:^)"))
 )
 
 
 ;; empty string at point
-;; Thanks Julian Bradford on XEmacs Beta
+;; Thanks Julian Bradfield on XEmacs Beta
 ;; <18652.54975.894512.880956 at krk.inf.ed.ac.uk>
 (with-string-as-buffer-contents "aáa"
   (goto-char (point-min))