Refactor codegen tests

- initialize environment only once in setUp()
- add comments on why some tests are disabled
- modify and rename some tests
- re-enable now working tests
- extract some tests into files with box()
- remove useless 'throws' declarations and commented code

compiler/testData/codegen/controlStructures/ifInWhile.kt

@@ -4,7 +4,6 @@ fun box() : String {
     val processors = Runtime.getRuntime()!!.availableProcessors()
     var threadNum = 1
     while(threadNum <= 1024) {
-        System.out?.println(threadNum)
         if(threadNum < 2 * processors)
             threadNum += 1
         else