- BrowseBox: Check Handle column-related invariants when adding a
   column:
   # only one handle column
   # it is the first

 - BrowseBox: Check column id-related invariants when adding a column:
   # Id is not the special "handle column" value
   # Id is not the special "invalid ID" value
   # unicity of the ID among columns

 - GetColumnId: return BROWSER_INVALIDID, not 0 (== id of handle
   column) for an invalid column; adapt code calling GetColumnId to
   this change.

 - Use the correct const or #define'd symbol instead of magic
   constants; introduce such a symbol if needed

 - General other miscellaneous cleanups:
   # Translation of comments
   # typo/spelling in comments, error messages and the like
   # parenthesise #define'd value
   # use SAL_MAX_UINT16 instead of USHRT_MAX where a sal_uInt16 is
     expected
   # BrowseBox::SetColumnTitle: nItemId is checked to be non-zero, so
     don't test if for zeroness again.