Fixes a build issue on some platforms, due to missing stdint.h

Fixes following compile error on my target platform:

    In file included from src/aio/poller.h:35:0,
                 from src/aio/poller.c:23:
    src/aio/poller_epoll.h:31:5: error: unknown type name 'uint32_t'
    make: *** [src/aio/poller.lo] Error 1

Shouldn't break anything else. MIT LICENSE naturally.