Add a regression test suite
Revert "addrinfo structs must be zeroed on OS X"

This wasn't the cause of the segfault described in #90. All fields are
already initialized to valid values.

This reverts commit e367a1da4dc55f17693e33a10fc7720bd8b0f4d6.
Fix a segfault in getAddrInfo on OS X

The OS X implementation of getaddrinfo has a bug where passing NULL for
servname and AI_NUMERICSERV in ai_flags causes a segfault. Linux does
not have this problem.