Require "-Xuse-experimental=kotlin.Experimental" on usages of Experimental

Since we're not yet sure of the design of Experimental/UseExperimental,
we're making them "experimental" themselves in some sense, in that the
user is required to provide the magic argument
"-Xuse-experimental=kotlin.Experimental" to be allowed to use either
Experimental or UseExperimental. This is more convenient than the
previous approach of "-language-version 1.3
-Xskip-metadata-version-check" because it's simpler and does not cause
pre-release binaries to be produced

libraries/stdlib/js/build.gradle

@@ -176,8 +176,8 @@ task compileJs(type: JavaExec) {
     doFirst {
         args = [jsOutputFile, rootDir, "$jsSrcDir/wrapper.js"] + inputFiles.collect { it.path }.sort() +
                (compileBuiltinsKotlin2Js.outputs.files.collect { it.path }.sort() +
-                compileKotlin2Js.outputs.files.collect { it.path }.sort() +
-                compileExperimentalKotlin2Js.outputs.files.collect { it.path }.sort()).findAll {
+                compileKotlin2Js.outputs.files.collect { it.path }.sort() /* +
+                compileExperimentalKotlin2Js.outputs.files.collect { it.path }.sort() */).findAll {
                    it.endsWith(".js") && !it.endsWith(".meta.js")
                }
     }
@@ -223,9 +223,9 @@ task compileJs(type: JavaExec) {
 
         sourceMapFile.text = groovy.json.JsonOutput.toJson(sourceMap)
 
-        file(jsOutputMetaFile).text = file(compileKotlin2Js.outputFile.path.replaceAll('\\.js$', '.meta.js')).text +
+        file(jsOutputMetaFile).text = file(compileKotlin2Js.outputFile.path.replaceAll('\\.js$', '.meta.js')).text /* +
                                       file(compileExperimentalKotlin2Js.outputFile.path.replaceAll('\\.js$', '.meta.js')).text
-                                              .replaceFirst(experimentalJsModuleName, 'kotlin')
+                                              .replaceFirst(experimentalJsModuleName, 'kotlin') */
     }
 }
 
@@ -357,4 +357,4 @@ task runMocha(type: NodeTask, dependsOn: [testClasses, installMocha, ':kotlin-te
     }
 }
 
-test.dependsOn runMocha
+test.dependsOn runMocha