Add ability to get a handle to a Context's Thread

Author: kyren

src/context.rs

@@ -234,6 +234,16 @@ impl<'lua> Context<'lua> {
         }
     }
 
+    /// Returns a handle to the active `Thread` for this `Context`.  For calls to `Lua::context`
+    /// this will be the main Lua thread, for `Context` parameters given to a callback, this will be
+    /// whatever Lua thread called the callback.
+    pub fn current_thread(self) -> Thread<'lua> {
+        unsafe {
+            ffi::lua_pushthread(self.state);
+            Thread(self.pop_ref())
+        }
+    }
+
     /// Calls the given function with a `Scope` parameter, giving the function the ability to create
     /// userdata and callbacks from rust types that are !Send or non-'static.
     ///

src/ffi.rs

@@ -118,6 +118,7 @@ extern "C" {
     pub fn lua_pushstring(state: *mut lua_State, s: *const c_char) -> *const c_char;
     pub fn lua_pushlightuserdata(state: *mut lua_State, data: *mut c_void);
     pub fn lua_pushcclosure(state: *mut lua_State, function: lua_CFunction, n: c_int);
+    pub fn lua_pushthread(state: *mut lua_State) -> c_int;
 
     pub fn lua_tointegerx(state: *mut lua_State, index: c_int, isnum: *mut c_int) -> lua_Integer;
     pub fn lua_tolstring(state: *mut lua_State, index: c_int, len: *mut usize) -> *const c_char;