Worked around a bug in libssh2 and raise the correct exception when libssh2_channel_read_ex() returns LIBSSH2_ERROR_EAGAIN.
Worked around a bug in libssh2 and raise the correct exception when libssh2_channel_read_ex() returns LIBSSH2_ERROR_EAGAIN.

snoack/ssh4py,snoack/ssh4py,snoack/ssh4py