libssh2_error() no longer allocates a string and only accepts a const
error string. I also made a lot of functions use the construct of
return libssh2_error(...) instead of having one call to
libssh2_error() and then a separate return call. In several of those
cases I then also changed the former -1 return code to a more
detailed one - something that I think will not change behaviors
anywhere but it's worth keeping an eye open for any such.
Solaris builds of libssh2-1.2.3 failed on both x64 and UltraSPARC
platforms because of two problems:
1) src/agent.c:145 sun is a reserved word when using the SUNWspro compiler
2) example/direct_tcpip.c:84 INADDR_NONE is not defined
