DelBit()

         Deactivates a bit selected from a byte

    Syntax:

         DelBit ( cByte, nBitPos ) -> cNewByte

         cByte   : Byte to be tratedtratar.
         nBitPos : Bit position inside the byte.

    Description:

         Puts to 0 a selected bit from a byte and returns the new byte.

    Return:

         New byte or Nil if cByte is not a character or nBitPos is not
         numeric.

    Example:

         cNewByte := BitBorra ( "C", 2 )