Use FindCurses to find curses libraries

- Some systems have the FindCurses.cmake module to find
  the curses/ncurses libraries using find_package(). And
  in some CheckLibraries is not very reliable, so as
  fallback FindCurses is now used if no other option
  works.
README: add note on RHEL/CentOS 6

Add note on autoconf >2.69 being required for compilation under
RHEL/CentOS.

Closes #178.
README.md: fix anchor tags for CentOS/RHEL section

MAke the use of anchor tags consistent for the change introduced in
5cd3cbe.
Merge pull request #184 from equalsraf/tb-curses

Use FindCurses.cmake as fallback to find curses libraries
Merge pull request #183 from rjw57/issue-178

README: add note on RHEL/CentOS 6
Use CMAKE_C_FLAGS variable to set compiler flags.

If the compiler is some GNU-alike variant, set the compiler flags to use
the gnu99 dialect of C and enable all warnings.

Non-GNU compilers may have to have their own magic added to set dialect
and enable warnings.

Closes #179.
README: add note on RHEL/CentOS 6

Add note on autoconf >2.69 being required for compilation under
RHEL/CentOS.

Closes #178.
README.md: fix anchor tags for CentOS/RHEL section

MAke the use of anchor tags consistent for the change introduced in
5cd3cbe.
Import luajit 2.0.2 source tree

This will be used for testing and in the future for reimplementing vimscript as
a compile-to-lua language.
Merge pull request #187 from rjw57/issue-179

Use CMAKE_C_FLAGS variable to set compiler flags.
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
Use cmake module instead of shared for nvim-test

On a Mac using shared creates libnvim-test.dylib which cannot be found
by the hardcoded .so extension in helpers.moon, causing the unittests to
fail. However, using module creates libnvim-test.so, allowing the tests
to run. There will still be problems running the tests on windows,
because both shared and module create dll file which will not be found
by in helpers.moon.