This changes the prototype of uv_run() from:
int uv_run(uv_loop_t* loop);
To:
int uv_run(uv_loop_t* loop, uv_run_mode mode);
Where `mode` is UV_RUN_DEFAULT, UV_RUN_ONCE or UV_RUN_NOWAIT.
Fixes#683.
Adds initial libuv build/platform support for AIX. Builds work using gcc or the
IBM XL C compiler using its gxlc wrapper. Platform support is added for
uv_hrtime, uv_exepath, uv_get_free_memory, uv_get_total_memory, uv_loadavg,
uv_uptime, uv_cpu_info, uv_interface_addresses.
