FUNCTION ISTHISAREA()

  Short:
  ------
  ISTHISAREA() Determines if expression is the name of a field
  in this area

  Returns:
  --------
  <lIsThisArea> => Is the expression a field in this
  area

  Syntax:
  -------
  ISTHISAREA(cExpress)

  Description:
  ------------
  Determines if <cExpress> contains the name of a field
  in this area.

  If <cExpress> contains an alias, the area of the
  alias will be checked.

  ISTHISAREA() first calls ISFIELD() to ensure the
  expression is a field name.

  If a field in another area is passed, and no alias is
  used, False will be returned.

  Examples:
  ---------
   ISTHISAREA("LASTNAME")             // actual field,  returns .t.

   ISTHISAREA("CUSTOMER->LASTNAME")  // actual field, returns .t.

   ISTHISAREA("LEFT(LNAME,5)")        // expression, returns  .f.

   ISTHISAREA("AGENT")                //field, but in another area. Returns .f.

  Notes:
  -------
  Companion functions are ISFIELD(), ISEDITABLE(),
  PARSFIELD(), PARSALIAS(), EXPBLOCK(), WORKBLOCK()

  Source:
  -------
  S_FIELDS.PRG