See header file and man pages for API. All documented API details work
and are tested in the 1560 test case.

Closes #2842

... and add "MAILINDEX".

As described in #2789, this is a suggested solution.  Changing UID=xx to
actually get mail with UID xx and add "MAILINDEX" to get a mail with a
special index in the mail box (old behavior).  So MAILINDEX=1 gives the
first non deleted mail in the mail box.

Fixes #2789
Closes #2815

Long live CURLE_PEER_FAILED_VERIFICATION

Approved-by: Daniel Gustafsson
Closes #2937

makes it not run in the CI builds

Closes #2941

Transparently. The related curl_multi_setopt() options all still returns
OK when pipelining is selected.

To re-enable the support, the single line change in lib/multi.c needs to
be reverted.

See docs/DEPRECATE.md

Closes #2705

"precheck command error" is not very helpful.

According to RFC6265 section 5.4, cookies with equal path lengths
SHOULD be sorted by creation-time (earlier first). This adds a
creation-time record to the cookie struct in order to make cookie
sorting more deterministic. The creation-time is defined as the
order of the cookies in the jar, the first cookie read fro the
jar being the oldest. The creation-time is thus not serialized
into the jar. Also remove the strcmp() matching in the sorting as
there is no lexicographic ordering in RFC6265. Existing tests are
updated to match.

Closes #2524

All these tests failed on Windows because something like
sftp://%HOSTIP:%SSHPORT%PWD/
expanded to
sftp://127.0.0.1:1234c:/msys64/home/bla/curl
and then curl complained about the port number ending with a letter.

Use the original POSIX path instead of the Windows path created in
checksystem to fix this.

Closes https://github.com/curl/curl/pull/2920