Relnotes: yes (subtle output/behavior change)

MFC r316938,r316953:

r316938:

savecore: fix space calculation with respect to `minfree` in check_space(..)

- Use strtoll(3) instead of atoi(3), because atoi(3) limits the
representable data to INT_MAX. Check the values received from
strtoll(3), trimming trailing whitespace off the end to maintain
POLA.
- Use `KiB` instead of `kB` when describing free space, total space,
etc. I am now fully aware of `KiB` being the IEC standard for 1024
bytes and `kB` being the IEC standard for 1000 bytes.
- Store available number of KiB in `available` so it can be more
easily queried and compared to ensure that there are enough KiB to
store the dump image on disk.
- Print out the reserved space on disk, per `minfree`, so end-users
can troubleshoot why check_space(..) is reporting that there isn't
enough free space.

Tested with: positive/negative cases (see review); make tinderbox

r316953:

Switch back to non-IEC units for 1024 bytes

I was swayed a little too quickly when I saw the wiki page discussing
kB vs KiB. Switch back as none of the code in base openly uses
IEC units via humanize_number(3) (which was my next step), and there's
a large degree of dislike with IEC vs more SI-like units.

MFC r316742:

Clarify units for mediasize and sectorsize in DoFile(..)

They're byte quantities.

MFC r316740:

Clarify `minfree` warning message in check_space(..)

- State that the units are kB.
- Be more complete/concise in terms of what is required (in this case
`minfree` must be at least `X`kB)

MFC r271720:

If fgets(3) fails in getbounds(), show strerror(3) if not an EOF. Also fix a
FILE* leak in getbounds().

PR: 192032
Approved by: re (gjb)

MFC r262775:
Log the name of the file that we failed to open rather than an
uninitialized buffer.

MFC: r264479

Fix double fclose() in an error case.

CID: 1006120
Found with: Coverity Prevent(tm)

MFC r271720:

If fgets(3) fails in getbounds(), show strerror(3) if not an EOF. Also fix a
FILE* leak in getbounds().

PR: 192032
Approved by: re (gjb)

MFC r262775:
Log the name of the file that we failed to open rather than an
uninitialized buffer.

MFC: r264479

Fix double fclose() in an error case.

CID: 1006120
Found with: Coverity Prevent(tm)