This is a partial backport of cb9da0bf and a backport of c9635349.

Because C doesn't like us to declare identifiers starting with an
underscore, Libevent 2.1 has renamed every such identifier.  The
only change that affects a public API is that the _EVENT_LOG_*
macros have been renamed to start with EVENT_LOG instead.  The old
names are still present, but deprecated.

I'm doing this backport because it represents the deprecation of a
Libevent 2.0 interface, and folks should have the opportunity to
write code that isn't deprecated and works with both 2.0 and 2.1.

This is necessary on msvc, to get the EVUTIL_EAI_* values defined properly

Oops; fix a merge conflict that got committed into event2/event-config.h.  Now msvc builds work again.

We've got to do this because doing otherwise seems to freak out
windows XP.

See 95e2455c for rationale.

I don't know why people use such ancient gcc versions, but the fix seems
straightforward enough to maybe just do it.

This takes its runtime back up a little again, but not so high as it
was before.  It appears to address the heisenbug issues of github
nmathewson/libevent issue #49.  So far.

MSVC apparently doesn't have a mode_t defined, though mingw does.

Found by Savg He.

Apparently, now that we have tests for it in main/common_timeout, we
can now see that it sometimes breaks referential integrity somehow.
Since I'd like to get 2.1.1-alpha out the door soon, I'm turning it
off for now.

Two calls to libevent_global_shutdown on your exit path shouldn't
result in a crash.

Require python version

What was I thinking?  The old function could handle heap-to-heap
transitions, and transitions within the same common timeout queue, but
it completely failed to handle heap/queue transitions, or transitions
between timeout queues.

Now, alas, it's complicated.  I should look hard at the assembly here
to see if it's actually better than the alternatives.