Enable js-flatten by default and provide -D js-unflatten to disable it.

Closes #3903.

common.ml

@@ -202,7 +202,7 @@ module Define = struct
 		| JavaVer
 		| JsClassic
 		| JsEs5
-		| JsFlatten
+		| JsUnflatten
 		| KeepOldOutput
 		| LoopUnrollMaxCost
 		| Macro
@@ -288,7 +288,7 @@ module Define = struct
 		| JavaVer -> ("java_ver", "<version:5-7> Sets the Java version to be targeted")
 		| JsClassic -> ("js_classic","Don't use a function wrapper and strict mode in JS output")
 		| JsEs5 -> ("js_es5","Generate JS for ES5-compliant runtimes")
-		| JsFlatten -> ("js_flatten","Generate classes to use fewer object property lookups")
+		| JsUnflatten -> ("js_unflatten","Generate nested objects for packages and types")
 		| KeepOldOutput -> ("keep_old_output","Keep old source files in the output directory (for C#/Java)")
 		| LoopUnrollMaxCost -> ("loop_unroll_max_cost","Maximum cost (number of expressions * iterations) before loop unrolling is canceled (default 250)")
 		| Macro -> ("macro","Defined when we compile code in the macro context")

genjs.ml

@@ -1196,7 +1196,7 @@ let alloc_ctx com =
 			mappings = Rbuffer.create 16;
 		};
 		js_modern = not (Common.defined com Define.JsClassic);
-		js_flatten = Common.defined com Define.JsFlatten;
+		js_flatten = not (Common.defined com Define.JsUnflatten);
 		statics = [];
 		inits = [];
 		current = null_class;