Minor autoconf tweaks

deprecate zmq_ctx_destroy in favor of zmq_ctx_term

AM_CONFIG_HEADER raises an 'obsolete error' with automake 1.13.

autotools warns that configure.in
should actually be named configure.ac

in order to avoid logical collisions with pre-existing notions of context destruction in bindings (czmq, pyzmq).

Clarified how icp:// works with zmq_bind

Fixed el5/el6 deps in RPM spec file / newline fix

Whitespace and comment cleanups

This reverts commit da0efaa8.

This reverts commit 8ba097f3.

allow XSUB/XPUB to send/recv messages unrelated to sub/unsub

zmq::xpub_t::xread_activated() – change to process messages without 0
or 1 prefix, but without affecting subscriptions

zmq::xsub_t::xsend() – change to send rather than discard messages
without 0 or 1 prefix, but without affecting subscriptions

Update documentation

Fix minor problem with cmake bulid

Make CMake build usable for other systems

Fix link errors when using -m32 with MinGW

The CPack NSIS installer was in a state where it would always give a
useless error. I think it was using stuff intended for running cpack
separately from cmake.

Fix warnings with ICC.

Make doc building option dependent on asciidoc being installed
Fix MSVC build requiring cygwin.
Don't use try_run to get the version