lowered autoconf requirement

Autoconf 2.59 works. And most notably it will not affect our releases
which are all prepared with newer autoconf.
issue-413: disable __thread usage on OSX

Because it was found that __thread variables access is compiled into
calls to tlv_get_addr which was found to call malloc. Because we
actually use thread-local storage from inside malloc it leads to stack
overflow. So we'll continue using pthreads API for that which is known
to work on OSX.