"*-*~1" => The last day of every month
"*-02~3..5" => The third, fourth, and fifth last days in February
"Mon 05~07/1" => The last Monday in May
Resolves#3861
Fixes:
```
==10750==
==10750== HEAP SUMMARY:
==10750== in use at exit: 96 bytes in 3 blocks
==10750== total heap usage: 1,711 allocs, 1,708 frees, 854,545 bytes
allocated
==10750==
==10750== 96 (64 direct, 32 indirect) bytes in 1 blocks are definitely
lost in loss record 3 of 3
==10750== at 0x4C2DA60: calloc (vg_replace_malloc.c:711)
==10750== by 0x4EB3BDA: calendar_spec_from_string
(calendarspec.c:771)
==10750== by 0x109675: test_hourly_bug_4031 (test-calendarspec.c:118)
==10750== by 0x10A00E: main (test-calendarspec.c:202)
==10750==
==10750== LEAK SUMMARY:
==10750== definitely lost: 64 bytes in 1 blocks
==10750== indirectly lost: 32 bytes in 2 blocks
==10750== possibly lost: 0 bytes in 0 blocks
==10750== still reachable: 0 bytes in 0 blocks
==10750== suppressed: 0 bytes in 0 blocks
==10750==
==10750== For counts of detected and suppressed errors, rerun with: -v
==10750== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
```
This patch improves parsing and generation of timestamps and calendar
specifications in two ways:
- The week day is now always printed in the abbreviated English form, instead
of the locale's setting. This makes sure we can always parse the week day
again, even if the locale is changed. Given that we don't follow locale
settings for printing timestamps in any other way either (for example, we
always use 24h syntax in order to make uniform parsing possible), it only
makes sense to also stick to a generic, non-localized form for the timestamp,
too.
- When parsing a timestamp, the local timezone (in its DST or non-DST name)
may be specified, in addition to "UTC". Other timezones are still not
supported however (not because we wouldn't want to, but mostly because libc
offers no nice API for that). In itself this brings no new features, however
it ensures that any locally formatted timestamp's timezone is also parsable
again.
These two changes ensure that the output of format_timestamp() may always be
passed to parse_timestamp() and results in the original input. The related
flavours for usec/UTC also work accordingly. Calendar specifications are
extended in a similar way.
The man page is updated accordingly, in particular this removes the claim that
timestamps systemd prints wouldn't be parsable by systemd. They are now.
The man page previously showed invalid timestamps as examples. This has been
removed, as the man page shouldn't be a unit test, where such negative examples
would be useful. The man page also no longer mentions the names of internal
functions, such as format_timestamp_us() or UNIX error codes such as EINVAL.
There are more than enough calls doing string manipulations to deserve
its own files, hence do something about it.
This patch also sorts the #include blocks of all files that needed to be
updated, according to the sorting suggestions from CODING_STYLE. Since
pretty much every file needs our string manipulation functions this
effectively means that most files have sorted #include blocks now.
Also touches a few unrelated include files.
