Finished polling API refactorization.

Knot.files

src/Makefile.am

src/common/fdset.c

src/common/fdset.h

src/common/fdset_epoll.c

src/common/fdset_poll.c

src/tests/common/fdset_tests.c

src/tests/common/fdset_tests.h

src/tests/common/os_fdset_tests.h

src/tests/unittests_main.c