Move CLSID_CMultiLanguage and CLSID_CMLangConvertCharset to mlang.idl.
Leave CLSID_CMLangString in regsvr.c as MSDN claims it is not supported anymore.

Spotted by David Hagood with test suggested by Dan Kegel.

- Accept MFT_MENU{BAR}BREAK, MFT_RADIOCHECK, MFT_RIGHTJUSTIFY, and
  MFT_RIGHTORDER in SetMenuItemInfo.
- InsertMenu, AppendMenu, ModifiyMenu: Accept MF_HILITE flag (undocumented).
- SetMenuItemInfo: Only use the lower word of the bitmap handle as
  documented in MSDN (Word 95 depends on this).
- The type MFT_RADIOCHECK cannot be set if only the checkmarks are
  modified with SetMenuItemInfo.
- New tests.