Fix compilation with WIN32_HAVE_CONDITION_VARIABLES enabled

Reported by Xiuqiang Jiang
Merge remote-tracking branch 'origin/patches-2.0'
minor documentation typos
Fix cut-and-paste err in whatsnew-2.1
Avoid leaking fds on evconnlistener with no callback set

There's no way to retrieve an fd from an evconnlistener whose
callback has been cleared, so we had better close any such fd.

Found by coverity; CID 739725.
Avoid double-close on getsockname error in evutil_ersatz_socketpair

Found by coverity; CID 739726
Merge remote-tracking branch 'origin/patches-2.0'
Fix comment to refer to sample/include.am correctly
Fix harmless clang enum warning
When EWOULDBLOCK is not EAGAIN, treat it as equivalent to it

Acording to http://stackoverflow.com/questions/7003234/which-systems-define-eagain-and-ewouldblock-as-different-values
there are some older unixes that distinguish these error.s
Fix typo : Dispatching instead of Dispaching
Fix a mistake in evbuffer_remove() arguments in example http server code

(commit message by nickm)
Merge remote-tracking branch 'origin/patches-2.0'
Implement EVUTIL_ERR_IS_EAGAIN on windows.