Made libssh2 logging more verbose when debugging is enabled.

easy handles are added to a multi handle, by avoiding the looping over all
the handles to find which one to remove.

by letting configure check for setmode and ifdef on HAVE_SETMODE. NOTE: non-
configure platforms that havve setmode() needs their hard-coded config.h files
fixed. I fixed the src/config-win32.h.

and they have to be non-NULL long before this check.
CID 22 in the coverity.com scan

it is missing
CID 5 in the coverity.com scan

CID 3 and 4 from the coverity.com scan.

cache, we must make sure not to derefence the NULL pointer...
CID 6 coverity.com scan

have not been properly defined to allow this! Instead of changing the defines
and break the ABI/API, I opted to modify the code to check for exact type
matches.
CID 10 coverity.com scan

happen when curl_multi_remove_handle() is called.
CID 13. coverity.com scan

anyway and we can just as well rely on it being valid.
CID 12, coverity.com scan

Removed the NULL check since the pointer must be valid already.

and added tests 290 and 291 to check.

Enable libssh2 tracing when ssh debugging is turned on.