Update net/rabbitmq-c to 0.8.0.

Added:
- SSL: peer certificate and hostname validation can now be
  controlled separately using amqp_ssl_socket_set_verify_peer and
  amqp_ssl_socket_set_verify_hostname.
- SSL: the desire SSL version range can now be specified using the
  amqp_ssl_socket_set_ssl_versions function.
- Add flags to SSL examples on controlling hostname verification.

Changed:
- SSL: SSLv2, and SSLv3 have been disabled by default.
- SSL: OpenSSL hostname validation has been improved.
- Win32 debug information is built with /Z7 on MSVC to embed debug
  info instead of using a .pdb

Fixed:
- Connection failure results in hang on Win32
- Rabbitmq-c may block when attempting to close an SSL socket
- amqp_parse_url does not correctly initialize default parameters
- x509 objects are leaked in verify_hostname
- TCP_NOPUSH doesn't work under cygwin

Deprecated
- SSL: amqp_ssl_socket_set_verify is being replaced by
- amqp_ssl_socket_set_verify_peer and
- amqp_ssl_socket_set_verify_hostname.

Removed:
- OpenVMS build system and related files.
- Unmaintained PolarSSL, CyaSSL, and gnuTLS SSL backends

(fhajny)