Remove Lua 5.1 for Lua 5.2 upgrade.

Issue #242.
Squashed 'external/lua/' content from commit aaf39ec

git-subtree-dir: external/lua
git-subtree-split: aaf39ecc16c688f6a3804477f9355651534ddec1
Merge commit '9899bf50d90b1c66882537b23365c619462ae7c2' as 'external/lua'

git subtree add --squash --prefix external/lua https://github.com/LuaDist/lua.git master

Issue #242.
LuaDist switched to master for Lua 5.2.

Issue #242.
Remove reference to liblua_static.

Issue #242.
Disable LuaDist binaries and install.

We don't need the lua and luac binaries; we're only interested in
liblua.  We also disable the install step since we'll handle that
ourselves.
Upgrade Win32 libs to Lua 5.2.

Issue #242.
Update class doc and copyright.
Update to Lua 5.2 API.

- The global table is now indexed via the registry.
- setfenv is no more.

Issue #242.
Rebuild Win32 Lua 5.2 DLLs with exports.

Previous build didn't have LUA_BUILD_AS_DLL defined, so there were no
exports from the DLL.

Issue #242.
Use the bundled Lua and Luabind on Win32.

This is so we use the exact same versions of Lua and Luabind on all
platforms.  Plus, it means we'll use the same Boost for Luabind as the
rest of the project.

Issue #242.
Remove prebuilt Lua and Luabind.

Issue #242.
Merge branch 'lua-5.2'

Conflicts:
	external/subtree.txt

Closes #242.