The new version of the lua client uses libmpack as a backend, and some test
scripts had to be updated to reflect that.

Luv is a simple lua binding to libuv, which is now used by neovim lua client.
The bundled luv installation a bit different from other dependencies in that it
is installed two times:

- The "BuildLuv.cmake" script downloads and installs a static version of luv
  using its normal cmake build script. This static version will be used later.
- Luv default rockspec is replaced with the alternate under the "rockspecs"
  directory(the alternate rockspec plays nicer with neovim build system)
- The alternate rockspec is used to build/install the lua module and make it
  available to lua scripts.

Also add a functionaltest-lua target to run the functional tests using the lua
interpreter and corresponding helper to top-level Makefile

Although UNIX is a registered trademark of The Open Group, it doesn't
really matter whether we refer to these systems as UNIX, Unix, or
Unix-like. So, for consistency, refer to them collectively as Unix.

Related:
http://www.greens.org/about/unix.html
http://www.unixica.com/html/unixunix.html

Otherwise the dynamic library is built also and find_library will prefer
that over the static one. That results in linking against the dynamic
library which will not be found after install.

This code:
  https://github.com/neovim/neovim/blob/8b3c399b6d7f4a277d80da4b29349fed944f7d46/third-party/CMakeLists.txt#L130
should prevent the above problem, but it doesn't hurt to be explicit.

So far luacheck's rockspec specified only the git protocol. Hence people
behind firewalls/proxies, that block port 9814, had trouble fetching this
dependency via luarocks.

The latest commit updated the rockspec to use either git or https. Thus common
workarounds like this are not needed anymore:

    git config --global url."https://".insteadOf git://

References #3769.

Source: https://github.com/mpeterv/luacheck
Docs:   http://luacheck.readthedocs.org/en/0.12.0/index.html

Run via "make testlint".