improved compatibility

[John W. Eaton]

I would like to eliminate the problems associated with the built-in
variables do_fortran_indexing, implicit_str_to_num_ok,
implicit_num_to_str_ok, and ok_to_lose_imaginary_part by replacing
them as follows:

  do_fortran_indexing        -->  warn_fortran_indexing
  implicit_num_to_str_ok     -->  warn_num_to_str
  implicit_str_to_num_ok     -->  warn_str_to_num
  do_to_lose_imaginary_part  -->  warn_imag_to_real

The code would be changed to work as if the old variables were all set
to TRUE, except that users could request warnings by setting the new
variables to TRUE (the default would be FALSE).

This change would improve compatibility with Matlab and eliminate some
of the problems we currently have with trying to write code that can
work no matter what the settings for these variables happen to be.

Comments?

jwe