Added sha1_feed_uint() when collecting entropy from an integer.

Also, when issuing a stat() or fstat() call, always hash the path or the fd
being probed.
sha1_feed_string(): also include the string pointer into the mix.
Removed declaration for unimplemented mingw_current_time().
Removed occurrence of "gint64", replacing by our "int64".
Added tm_precise_time() and tm_precise_granularity().
Regenerated Configure for detecting the BFD library even if no -liberty.
Windows: added emulated clock_gettime() and clock_getres().
Switched to tm_precise_time() in entropy gathering routines.
Added ENTROPY_KISS_MULT, making sure the 'c' parameter is less than that.

For the KISS PRNG, the 'c' parameter must not be a random 32-bit number but is
constrained by the KISS multiplier, since this is the carry of a multiplication
by ENTROPY_KISS_MULT of a 32-bit number.
entropy_seed(): throw current precise time into the mix before reseeding rand31.
Made sure the initial "carry" of the CMWC state is correctly initialized.
Added comments stating that entropy gathering routines rely on AJE later on.

The entropy collection only probes the environment until the AJE layer is up.
Once the global AJE state has been initialized, it becomes the source of entropy
for the application.
Use entropy_minirand() instead of the weaker rand31_u32() to seed entropy.