[PATCH] explorer: fix for x64 build

There is CustomizeClassicProc defined in \base\shell\explorer\startmnucust.cpp . It used as DLGPROC - so it must return INT_PTR, but it returns BOOL. it works because on 32-bit build INT_PTR and BOOL are both int , but on 64-bit build INT_PTR is __int64 and BOOL is just int .
Tested on msvc2012 x64 build