This is Hoi-Ho Chan's patch with some minor fixes by me. There
are some potential issues in this, but none worse than we can
sort out on the list and over time.

The main change is to allow input from user-specified methods,
when they are specified with CURLOPT_READFUNCTION.
All calls to fflush(stdout) in telnet.c were removed, which makes
using 'curl telnet://foo.com' painful since prompts and other data
are not always returned to the user promptly.  Use
'curl --no-buffer telnet://foo.com

' instead.  In general,
the user should have their CURLOPT_WRITEFUNCTION do a fflush
for interactive use.

Also fix assumption that reading from stdin never returns < 0.
Old code could crash in that case.

Call progress functions in telnet main loop.

Signed-off-by: Ben Greear <greearb@candelatech.com>

The necessary libssh2 functions require libssh2 1.2.5 or later.

Make sure we don't call memcpy() if the argument is NULL even
though we also passed a zero length then, as the clang analyzer
whined and we want to limit warnings (even false positives) when
they're this easy to fix.

The change of (char) to (unsigned char) will fix long user names
and passwords on systems that have the char type signed by
default.

This function could only return CURLE_OK and by changing it to
a void instead, we can simplify code all over.

Simplified the code by removing a local variable completely.

This makes the code flow more obvious and reacts on the return
code properly, even if the code acted the same way before.

When multi interface is used, the SSL handshake is no longer
blocking when GnuTLS is used.

The recent overhaul of the SSL recv function made this treat a
zero returned from gnutls_record_recv() as an error, and this
caused our HTTPS test cases to fail. We leave it to upper layer
code to detect if an EOF is a problem or not.

No resolver anymore needs to use AI_CANONNAME and do reverse
lookups.  We should work hard to avoid having code that relies on
it.

This code would previously use dns_entry->addr->ai_canonname
instead of the given host name, which caused us grief and
problems since not all our resolver options do the reverse lookup
and I would also guess that it caused problems with KRB5/GSS with
virtual name-based hosts. Now the host name from the URL is used.