Use GNU gettext from homebrew on Mac if available
Improve libintl detection and linking.

This makes it so that a self-installed libintl is now detected and used.
It also attempts to locate a homebrew version of the library, if that
exists.
CMakeLists: Use nvim target name
CMakeLists: Improve handling of libintl

by refactoring it into a separate CMake module
Add basic infrastructure for unit testing

Tests will be written using the [moonscript](http://moonscript.org/) language,
a lua 'dialect' that is whitespace-significant and has a syntax similar to
coffeescript. The test framework used is [busted](http://olivinelabs.com/busted/),
a bdd framework for lua/moonscript.

Luajit has a nice ffi module, which lets lua programs link shared libraries and
call it's functions without writing any C code.

To take advantage of this fact for testing C functions, a new target was added
to CMakeLists.txt, which compiles neovim as a shared library that is loaded by
the process running the tests.

This commit adds necessary code for downloading and installing a lua package
manager(luarocks) locally. It wasn't added as a subtree because there are quite
a few blobs in its source tree.
Add more example unit tests and run with travis
Disable unit tests until fixed for travis
Compile libuv with -fPIC.

This is needed so that th unit tests library compiles on 64-bit machines
correctly.
Add unit test running to travis again
MAKE: ask gnulikes to warn and be pedantic

It seems clang 3.4 thinks the codebase is in fantastic shape and gcc 4.9.0
has only minor niggles, which I will fix in a follow-up commit
fix uninitialized member warning

In DEBUG mode the expr member doesn't get properly initialized to NULL.
fix warnings about directive inside of macro's

On some platforms/compilers, sprintf is a macro. Putting macro directives
inside of a macro is unportable and gcc 4.9 warns about that.
fix signed vs. unsigned comparison warning

The in-memory table will luckily not even come close to the limits imposed
by ssize_t. If it ever reaches that, we've got bigger problems.