Updated 6/29/00 by TDC.

--- Rewrite all contractions involving a shift13 to avoid reassignment of
pointers.

--- Rewrite all contractions involving a shift31 to resort the data and use
the BLAS DGEMM.

--- Add checks for NULL pointers returned by dpd_block_matrix().  This will
serve as the flag for out-of-core contraction algorithms.

--- Add memcpy() or just a file pointer copy to "case 12" in
dpd_buf4_mat_irrep_rd_block(), dpd_buf4_mat_irrep_wrt_block(),
dpd_buf4_mat_irrep_row_rd(), dpd_buf4_mat_irrep_row_wrt(), others?

--- Add documentation for file4_cache.c functions.
