FIX: memory leak in amqp_new_connection

amqp_new_connection will fail to free the amqp_connection_state_t object
that is allocated when amqp_tune_connection fails with ERROR_NO_MEMORY.
This fixes that
FIX: missing va_end in amqp_login* functions

Be sure to va_end any va_start'ed va_lists in amqp_login and
amqp_login_with_properties