Scribble crashes in the presence of assingments from storage pointers to storage pointers

[cd1m0]

Consider the following sample:

contract Foo {
    struct S {
        uint[] arr;
    }

    function main(S storage v) private {
        S storage v1 = v;
    }
}

Running scribble (up to version 0.5.5) on this produces the following crash:

/home/dimo/work/consensys/scribble-clean/dist/instrumenter/state_vars.js:321
        throw new Error(`Unexpected RHS element ${__1.print(rhs)} in assignment to state var pointer`);
        ^

Error: Unexpected RHS element v in assignment to state var pointer
    at gatherRHSVars (/home/dimo/work/consensys/scribble-clean/dist/instrumenter/state_vars.js:321:15)
    at Object.findAliasedStateVars (/home/dimo/work/consensys/scribble-clean/dist/instrumenter/state_vars.js:350:26)
    at new InstrumentationContext (/home/dimo/work/consensys/scribble-clean/dist/instrumenter/instrumentation_context.js:231:38)
    at Object.<anonymous> (/home/dimo/work/consensys/scribble-clean/dist/bin/scribble.js:487:26)
    at Module._compile (internal/modules/cjs/loader.js:1015:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1035:10)
    at Module.load (internal/modules/cjs/loader.js:879:32)
    at Function.Module._load (internal/modules/cjs/loader.js:724:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:60:12)
    at internal/main/run_main_module.js:17:47

The issue is that the logic of this does not account for the case where the RHS of an assignment to a storage pointer is an Identifier, but its not a direct reference to a state var. This happens when the RHS is another storage pointer. (see code below):

    /**
     * Given a potentially complex RHS expression, return the list of
     * state variable declarations that it may alias
     */
    const gatherRHSVars = (rhs: Expression): VariableDeclaration[] => {
        if (isStateVarRef(rhs)) { // <-- This check needs to handle all Identifiers
            return [rhs.vReferencedDeclaration as VariableDeclaration];
        }

...
        throw new Error(`Unexpected RHS element ${print(rhs)} in assignment to state var pointer`);
    };

[cd1m0]

Fixed with #87