keep flash8 Boot and temporarily activate DCE for unit tests to investigate some Java DCE issues

std/flash8/Boot.hx

@@ -24,6 +24,7 @@
  */
 package flash;
 
+@:keep
 class Boot {
 
 	private static var def_color = 0;

tests/unit/Test.hx

@@ -1,6 +1,6 @@
 package unit;
 
-class Test #if swf_mark implements mt.Protect #end #if as3 implements haxe.Public #end {
+@:keepSub class Test #if swf_mark implements mt.Protect #end #if as3 implements haxe.Public #end {
 
 	public function new() {
 	}

tests/unit/params.hxml

@@ -2,4 +2,5 @@
 -cp ..
 -resource res1.txt
 -resource res2.bin
---no-opt
+--no-opt
+--dead-code-elimination