random: Add more bytes to the pool in addition to the seed file.

* random/random-csprng.c (read_seed_file): Read 128 or 32 butes
depending on whether we have the Jitter RNG.

These are actually 3 changes:

• We use GCRY_STRONG_RANDOM instead GCRY_WEAK_RANDOM, which we used for historical reasons. However the entropy gather modules handle both identical; that is reading from /dev/urandom. Only GCRY_VERY_STRONG_RANDOM would use a blocking read from /dev/random.

• We increase the number of extra buts from 128 or 256.

• If the Jitter RNG is available we assume that a fast entropy source is available and thus we read 4 times more entropy (1024 bits).

Note that on Windows GnuPG tests in DE-VS mode that the Jitter RNG is
available and properly working. Thus we will add 1024 bits in
addition to the state read from the seed file.

• Signed-off-by: Werner Koch <wk@gnupg.org>