+ implementation of unit dbf_wtil now split into target dependant include files, added implementation for OS/2

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28893 3ad0048d-3df7-0310-abae-a5850022a9f2
  * unit dbf_dbffile now compilable under OS/2

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28894 3ad0048d-3df7-0310-abae-a5850022a9f2
  * dbase support now enabled for OS/2

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@28895 3ad0048d-3df7-0310-abae-a5850022a9f2