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.

--proto tells curl to use the listed protocols for its initial
retrieval

--proto-redir tells curl to use the listed protocols after a
redirect

Also tweaked comments in certain examples using curl_multi_fdset().

The -O option caused curl to crash on windows and DOS due to the
tool writing out of boundary memory.

The feature that uses the file name given in a
Content-disposition: header didn't properly skip trailing
carriage returns and linefeed characters from the end of the file
name when it was given without quotes.

Make the function call with (void) as we don't care about the
return code.

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.