The size of the first level reference count table is given in terms of the
number of clusters it occupies. It's not the number of entries in the table,
as it is for the L1 cluster table.

For small images, the two are the same. With the unit tests based on small
images, this change has therefore no effect on the unit test.  For larger
images (like the FreeBSD 10.1-RELEASE image), this gives a discrepancy that
actually shows up when running "qemu-img check".

Bump the version number of mkimg.

While here, fix a white-space bug.

MFC after: 1 week
For architectures where time_t is wide enough, in particular, 64bit
platforms, avoid overflow after year 2038 in clock_ct_to_ts().

PR:	195868
Reviewed by:	bde
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week