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
The required low-level logic was already available as part of
`libssh2` (via `LIBSSH2_FLAG_COMPRESS` `libssh2_session_flag()`[1]
option.)
This patch adds the new `libcurl` option `CURLOPT_SSH_COMPRESSION`
(boolean) and the new `curl` command-line option `--compressed-ssh`
to request this `libssh2` feature. To have compression enabled, it
is required that the SSH server supports a (zlib) compatible
compression method and that `libssh2` was built with `zlib` support
enabled.
[1] https://www.libssh2.org/libssh2_session_flag.html
Ref: https://github.com/curl/curl/issues/1732
Closes https://github.com/curl/curl/pull/1735
