Add coverity_scan coverage to travis config
Fixes for travis-ci configuration.
MinGW : missing ssize_t typedef
Mingw: specify WINVER 0x0502 when unspecified.

WINVER 0x0502 is WinXP SP2
CMake: Add -DHAVE_CONFIG_H to tests/*.c

test_hostcheck includes a file which includes amqp_private.h which needs
config.h.
Use poll(2) for timeouts on socket

Use poll(2) instead of select(2) to do timeout operations on sockets. This helps
with the situation where the fd is larger than FD_MAXSIZE.

Fixes #168