Fix mixed package protection in std.regex

This code worked before because of bug in qualifiied package protection
implementation in DMD which resulted in merging protection levels of
aggregates and their member symbols.

std/regex/internal/ir.d

@@ -489,7 +489,7 @@ struct Regex(Char)
         return NamedGroupRange(dict, 0, dict.length);
     }
 
-package:
+package(std.regex):
     import std.regex.internal.kickstart; //TODO: get rid of this dependency
     NamedGroup[] dict;  //maps name -> user group number
     uint ngroup;        //number of internal groups
@@ -546,7 +546,7 @@ package:
 //@@@BUG@@@ (unreduced) - public makes it inaccessible in std.regex.package (!)
 /*public*/ struct StaticRegex(Char)
 {
-package:
+package(std.regex):
     import std.regex.internal.backtracking;
     alias Matcher = BacktrackingMatcher!(true);
     alias MatchFn = bool function(ref Matcher!Char) @trusted;
@@ -565,7 +565,7 @@ public:
 
 // The stuff below this point is temporarrily part of IR module
 // but may need better place in the future (all internals)
-package:
+package(std.regex):
 
 //Simple UTF-string abstraction compatible with stream interface
 struct Input(Char)