osrm-backend: luabind check doesn't find 5.2

With the new luabind check in dev branch, compilation fails with:

-- Looking for Luabind...
-- Found Luabind: /usr/lib/libluabind.so  
-- Found Luabind: /usr/lib/libluabind.so
-- Found Lua52: /usr/lib/x86_64-linux-gnu/liblua5.2.so;/usr/lib/x86_64-linux-gnu/libm.so  
-- Looking for LuaJIT 5.2
-- Could NOT find LUAJIT (missing:  LUAJIT_LIBRARIES LUAJIT_INCLUDE_DIR) 
-- Performing Test LUABIND_WORKS
-- Performing Test LUABIND_WORKS - Failed
-- Luabind/Lua5.2 not feasible, falling back to Lua 5.1.
CMake Error at /usr/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:108 (message):
  Could NOT find Lua51 (missing: LUA_INCLUDE_DIR)
Call Stack (most recent call first):
  /usr/share/cmake-2.8/Modules/FindPackageHandleStandardArgs.cmake:315 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-2.8/Modules/FindLua51.cmake:76 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  cmake/check_luabind.cmake:24 (find_package)
  CMakeLists.txt:229 (include)

If I check out the commit before the new luabind check was introduced, b1bbf2ef8412baea127c23f5fa029ffe397c552d, compilation works:

-- Found Lua52: /usr/lib/x86_64-linux-gnu/liblua5.2.so;/usr/lib/x86_64-linux-gnu/libm.so  
-- Looking for LuaJIT 5.2
-- Could NOT find LUAJIT (missing:  LUAJIT_LIBRARIES LUAJIT_INCLUDE_DIR) 
-- Looking for Luabind...
-- Found Luabind: /usr/lib/libluabind.so  
-- Found Luabind: /usr/lib/libluabind.so
-- Found LibXml2: /usr/lib/x86_64-linux-gnu/libxml2.so (found version "2.9.1") 
...

The resulting binaries work as expected when compiling this older version.

Ping @alex85k.