Task 2. Add indices to for loop intention

Task2.md

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+Task 2
+======
+
+We are going to add an intention action for turning a normal for-loop
+
+    for (x in list) {
+        ....
+    }
+
+into a for loop with indices
+
+    for ((i, x) in list.withIndices()) {
+        ....
+    }
+
+Background
+----------
+
+[How to create intention actions](http://confluence.jetbrains.com/display/IDEADEV/Creation+of+Intention+Action)
+(some extra information: [Language Plugins](http://confluence.jetbrains.com/display/IDEADEV/Developing+Custom+Language+Plugins+for+IntelliJ+IDEA))
+
+Code transformations are done by creating a new PSI node (basically, PSI=Syntax Tree) and replacing the old node by the new one.
+To create a new node, it's best to compose some text and run the parser on it. This is done using `JetPsiFactory` class.
+
+Hint: when you need an instance of type `Project`, you can obtain it from any descendant of `JetElement` or `PsiElement`
+
+Simplest version
+----------------
+
+Make it work for any for-loop, regardless of the type of the range.
+Use this commit as an example:
+
+    d198465 Add an intention to simplify negated binary expressions
+
+(Other examples can be found in the same directory: idea/src/org/jetbrains/jet/plugin/intentions)
+
+Analyze the cases, where the intention should not be applicable, except for the case of `withIndices()` being unavailable.
+
+More Advanced Version
+---------------------
+
+Make the intention inapplicable when the range expression's type is not a subtype of `Iterable<Any?>`.
+
+To see how to retrieve a type of an expression, see the `ShowExpressionTypeAction` class (Navigate -> Class... -> <class name>).
+
+To check suptyping use a function called `isSubtypeOf()` (Navigate -> Symbol -> <function name>)
+
+To construct a type symbol for `Iterable<Any?>` use
+ - `KotlinBuiltIns`
+ - `ClassDescriptor::getDefaultType()`
+ - `JetType::getConstructor().getParameters()`
+ - `TypeSubstitutor`
+
+Even More Advanced
+------------------
+
+- Sometimes the range expression should be parenthesized before you can add `.withIndices()`, e.g.:
+
+```
+    for (x in list1 + list2) {
+        ....
+    }
+```
+- Check out `_Mapping.kt` to make the applicability condition more precise
+
+Really Advanced
+---------------
+
+Allow the user to choose the name of the index variable. Use `ReplaceItWithExplicitFunctionLiteralParamIntention` as an example
+
+
+Don't forget to add tests
+-------------------------