Bug in devel version of mpn_set_str

[Torbjorn Granlund]

The development version of mpn/generic/set_str.c linked from
http://gmplib.org/devel/ has had an bug that could cause it to inject
garbage into result numbers.  The bug was triggered by long chunks of
zeros, at least a few thousands, in the input.  This caused a block
size to become zero, which wasn't handled properly.

There is now an updated version at the same place.

The GMP test suite did not catch this error.  Test suite shortcomings
are always somewhat worrying.  I've now updated the test suite to
check radix conversions more exhaustively.

(Note that this bug does not affect any released verion of GMP.)

-- 
Torbjörn