Add clang-format configuration
Revert the C++ compatibility changes.

- These only make it harder to track the official Apple version at opensource.apple.com.
- Visual Studio 2013 supports C99 now
- For dispatch i/o, we could get GCC compatibility by compiling this file only as C++, and substituting C++11 lambdas for blocks with some preprocessor shenanigans
Rename some constants for cross-platform compat
Rename #define to match Mavericks source tree
Add Travis CI config
Simplify build system

- Remove automake build system -- I don't have the knowledge to maintain
  it
- Remove Darwin-specific stuff from CMake build system -- this was
  always superfluous, and never tested.
- Combine the various CMake helper functions into a single file
Add support for eventfd even if glibc doesn't expose it

RHEL 5.10 appears to support eventfd, just not via glibc. We syscall()
it instead.
WIP