Toom sqr recursion

[Torbjorn Granlund]

Torbjorn Granlund <tg at gmplib.org> writes:

  I just spotted that we're not depending on SQR_BASECASE_THRESHOLD in any
  of the recursive toomN_sqr calls.  I think we should, at least from
  toom2_sqr.

And in toom44_mul.c and toom4_sqr.c we set MAYBE_*_toom4* using
MUL_FFT_THRESHOLD when we should really consider TOOM6 or (if TOOM6 = 0)
TOOM8.  This was forgotten when the 6H and 8H code was merged.

-- 
Torbjörn