Consolidate the three different charset headers

There are three headers, charset.h/charset_info.h/global_charset_info.h, that do varying amounts of exactly the same thing. They should be considated, or at least usage of one over the other should be documented and made clear. Oh - and they should be put into the drizzled namespace. While you're looking at it, look at drizzled/internal/my_uctype.h and drizzled/internal/t_ctype.h to see if there's any general way to make the whole thing suck less ass.