Fix that "ab" =~ /(?!^a).*b/ didn't match (Issue #44)

See also: https://bugs.ruby-lang.org/issues/9728

Optimization for '.*' was wrong. Optimization should be disabled not
only for /(?<=x).*/ but also for /(?!x).*/.

regcomp.c

@@ -4512,6 +4512,9 @@ concat_opt_anc_info(OptAncInfo* to, OptAncInfo* left, OptAncInfo* right,
   if (right_len == 0) {
     to->right_anchor |= left->right_anchor;
   }
+  else {
+    to->right_anchor |= (left->right_anchor & ANCHOR_PREC_READ_NOT);
+  }
 }
 
 static int
@@ -5085,7 +5088,8 @@ optimize_node_left(Node* node, NodeOptInfo* opt, OptEnv* env)
     case ANCHOR_END_BUF:
     case ANCHOR_SEMI_END_BUF:
     case ANCHOR_END_LINE:
-    case ANCHOR_LOOK_BEHIND: /* just for (?<=x).* */
+    case ANCHOR_LOOK_BEHIND:	/* just for (?<=x).* */
+    case ANCHOR_PREC_READ_NOT:	/* just for (?!x).* */
       add_opt_anc_info(&opt->anc, NANCHOR(node)->type);
       break;
 
@@ -5108,7 +5112,6 @@ optimize_node_left(Node* node, NodeOptInfo* opt, OptEnv* env)
       }
       break;
 
-    case ANCHOR_PREC_READ_NOT:
     case ANCHOR_LOOK_BEHIND_NOT:
       break;
     }
@@ -5374,7 +5377,8 @@ set_optimize_info_from_tree(Node* node, regex_t* reg, ScanEnv* scan_env)
         ANCHOR_BEGIN_POSITION | ANCHOR_ANYCHAR_STAR | ANCHOR_ANYCHAR_STAR_ML |
         ANCHOR_LOOK_BEHIND);
 
-  reg->anchor |= opt.anc.right_anchor & (ANCHOR_END_BUF | ANCHOR_SEMI_END_BUF);
+  reg->anchor |= opt.anc.right_anchor & (ANCHOR_END_BUF | ANCHOR_SEMI_END_BUF |
+	ANCHOR_PREC_READ_NOT);
 
   if (reg->anchor & (ANCHOR_END_BUF | ANCHOR_SEMI_END_BUF)) {
     reg->anchor_dmin = opt.len.min;

regexec.c

@@ -4188,7 +4188,7 @@ onig_search_gpos(regex_t* reg, const UChar* str, const UChar* end,
             prev = s;
             s += enclen(reg->enc, s);
 
-            if ((reg->anchor & ANCHOR_LOOK_BEHIND) == 0) {
+            if ((reg->anchor & (ANCHOR_LOOK_BEHIND | ANCHOR_PREC_READ_NOT)) == 0) {
               while (!ONIGENC_IS_MBC_NEWLINE_EX(reg->enc, prev, str, end, reg->options, 0)
                      && s < range) {
                 prev = s;