TDbf 6.9.0 released

This is a 7.0 beta release.

Note that indexes are not backward compatible!

Full log of changes:
- BDE compatible index collation: MDX/NDXes have to be rebuilt!
(thx sstewart for generating collation tables)
- fix use long char fields check icw foxpro (thx rpoverdijk)
- fix TDbf.GetRecNo AV when no file open
- remove UseFloatFields, delphi 3 will use float fields, others not
- fix size/precision truncation when opening foxpro B-type fields (thx nring)
- foxbase memo is 10 character index, sizes 4 and 10 are valid (thx majky)
- add int64 to string conversion in expression parser function STR
- fix nativeformat for tdbf.getfielddata(A,B) users
- allow later defined expression variables to have same name as
already defined function
- third parameter in substr function is optional now
- expression parser distinguishes between function() and variable, =no brackets
- updated bcb 4 packages files from troy dalton
- fix write blob B-type field for non-foxpro (thx leexgone)
- fix win64 compatibility