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.

src/CMakeLists.txt

@@ -13,6 +13,7 @@ list(APPEND NEOVIM_SOURCES "${PROJECT_BINARY_DIR}/config/auto/pathdef.c")
 file( GLOB OS_SOURCES os/*.c )
 
 add_executable (nvim ${NEOVIM_SOURCES} ${OS_SOURCES})
+add_library (nvim-test SHARED ${NEOVIM_SOURCES} ${OS_SOURCES}) 
 
 # The libraries we link against for nvim
 set(NVIM_LINK_LIBRARIES m ${LibUV_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT})
@@ -28,19 +29,23 @@ if (LibIntl_FOUND)
 endif()
 
 target_link_libraries (nvim ${NVIM_LINK_LIBRARIES})
+target_link_libraries (nvim-test ${NVIM_LINK_LIBRARIES})
 
 include(CheckLibraryExists)
 check_library_exists(termcap tgetent "" HAVE_LIBTERMCAP)
 
 if (HAVE_LIBTERMCAP)
   target_link_libraries(nvim termcap)
+  target_link_libraries(nvim-test termcap)
 else()
   check_library_exists(curses tgetent "" HAVE_LIBCURSES)
   if (HAVE_LIBCURSES)
     target_link_libraries(nvim curses)
+    target_link_libraries(nvim-test curses)
   else()
     find_package(Curses REQUIRED)
     target_link_libraries(nvim ${CURSES_LIBRARIES})
+    target_link_libraries(nvim-test ${CURSES_LIBRARIES})
   endif()
 endif()