Revert "* re.c (rb_reg_initialize): don't set US-ASCII to regexp"

This reverts commit r30058.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@30059 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,9 +1,3 @@
-Fri Dec  3 01:55:19 2010  NARUSE, Yui  <naruse@ruby-lang.org>
-
-	* re.c (rb_reg_initialize): don't set US-ASCII to regexp
-	  when parser make initially compile a regexp.
-	  Usually regexp are used for the same of its script encoding.
-
 Fri Dec  3 01:52:43 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* encoding.c (enc_alias_internal): use xfree instead of free.

re.c

@@ -2403,6 +2403,9 @@ rb_reg_initialize(VALUE obj, const char *s, long len, rb_encoding *enc,
 	    enc = fixed_enc;
 	}
     }
+    else if (!(options & ARG_ENCODING_FIXED)) {
+       enc = rb_usascii_encoding();
+    }
 
     rb_enc_associate((VALUE)re, enc);
     if ((options & ARG_ENCODING_FIXED) || fixed_enc) {