Make sure not to break build because of warnings.

Disable warnings by default. Use the LUABIND_ENABLE_WARNINGS CMake variable to
enable them ("disable" here means not to touch compiler defaults for warnings,
which on MSVC is equivalent to /W3).

Additionally, if warnings are enabled, make sure not to request warnings added
in g++ 4.3 on older versions (caused "error: unrecognized command line
option").
Scoped enum support: Check also for BOOST_NO_CXX11_HDR_TYPE_TRAITS.
Build: Add option()s for existing variables.
FindLua52.cmake: Mark internal variables as advanced.
Add option to build luabind as a shared library.

If you get crashes on Windows/MSVC in _CrtIsValidHeapPointer(), you need to
link Lua dynamically. This may also be necessary on other platforms.

The problem is probably that Lua is linked twice otherwise: Once to
luabind09.dll/.so and a second time to the application using it.