update FLINT to r1075, add spkg-check

[mabshoff]

The current FLINT release (r1072) has some problems on Core Duos that only show with FLINT's extensive test suite.

In addition Bill wrote me:

Actually I've got no idea how to create an spkg-check script. But the
things you would type at the command line, supposing you were in the
FLINT source tree in the trunk directory are:

make -Bj test
./mpn_extras-test
./ZmodF-test
./ZmodF_mul-test
./ZmodF_poly-test
./fmpz-test
./fmpz_poly-test

Those tests take about 6.5 minutes to run on sage.math, but we should run the tests per default for at least on release cycle (2.8.14) and disable them right before the final release. This will help Bill to shake out the last esoteric bug before the 1.0 release. The current Sage doctests don't even push the envelope.

Cheers,

Michael