A better fix for wxHash{Map,Set} with g++ 4.7.

This reverts r70556, i.e. removes the scope operators added by it to all
WX_DECLARE_HASH_{MAP,SET} macros, and implements a workaround for the problem
due to the use of empty base class optimization in g++ 4.7 standard library
implementations inside the macros themselves by prepending the hasher and
comparator classes with explicit "struct".

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72297 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -530,6 +530,7 @@ Major new features in this release
 All:
 
 - Add wxDir::Close() method (Silverstorm82).
+- Fix compilation of wxHash{Map,Set} with g++ 4.7 (Nathan Ridge).
 
 All (GUI):