check_ssh using libssh to verify host fingerprint and openssh version

    if libssh is not found, the fingerprint / openssh-version-detection functions are not compiled in.
    for backward compatibility the parameters of original check_ssh stay untouched
    for checking the fingerprint && || the openssh version use -f and or -o

    to check against known_hosts file use -f known_host

    sample calls:
        #checks if SSH fingerprint is stored in local known hosts
        ./check_ssh -f known_hosts  localhost

        #checks if SSH fingerprint is stored in local known hosts, and version is >= 5.5
        ./check_ssh -f known_hosts  -o 5.5 localhost

        #checks if SSH fingerprint is equal the print supplied with -f
        ./check_ssh -f  a2:47:e8:83:d9:8b:f5:c4:19:23:47:0d:e0:bf:a8:26  localhost

        #checks if SSH fingerprint is equal the print supplied with -f and version is >= 5.5
        ./check_ssh -f  a2:47:e8:83:d9:8b:f5:c4:19:23:47:0d:e0:bf:a8:26  -o 5.5 localhost

        #check for SSH version
        ./check_ssh -o 5.5 localhost
Merge remote-tracking branch 'dermoth/pu'

Conflicts:
	configure.in
	plugins/Makefile.am
	plugins/check_ssh.c