formally declare luaskia extern guy, and then define it

BUG=

Review URL: https://codereview.chromium.org/17503003

git-svn-id: http://skia.googlecode.com/svn/trunk@9705 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index 296229b..4f662ca 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -950,6 +950,7 @@
     REG_CLASS(L, SkTypeface);
 }
 
+extern "C" int luaopen_skia(lua_State* L);
 extern "C" int luaopen_skia(lua_State* L) {
     SkLua::Load(L);
     return 0;