Should not try to attach to modules that export primitives

[elicwhite]

When people use rewire, they wouldn't typically try to explicitly rewire modules that export primitives.

However, since reweireify, rewire-global, and babel-plugin-rewire all get injected to every module, this needs to not blow up on objects that can't be attached to.

rewireify and rewire-global use Object.isExtensible instead of the type check. The behavior of Object.isExtensible change from es5 to es6. In ES5, it would throw if given something that was not an object. in ES6, it returns false. rewireify and rewire-global all run in the browser and all modern browsers have the es6 version of the functionality. Node 0.12 has the es5 functionality, so we need to use the type check instead.

I added a test to make sure that it doesn't blow up on modules that return sealed objects. Object.defineProperty will run and not throw, but won't actually modify the object.

[elicwhite]

This PR makes all of my tests pass for rewire-global while reusing getImportGlobalsSrc and getDefinePropertySrc.

[elicwhite]

@jhnns I rebased this from master. What are your thoughts on this? I'd like to be able to make these modules share more and have a consistent API.

[elicwhite]

@jhnns Bump.

[jhnns]

In ES5, it would throw if given something that was not an object

Does this mean that null will throw on node 0.12?

[jhnns]

Btw: Thx for your PR 👍. I'll merge it asap.

[elicwhite]

$ nvm use 0.12
Now using node v0.12.7
$ node
> Object.isExtensible(null)
TypeError: Object.isExtensible called on non-object
    at Function.isExtensible (native)
    at repl:1:8
    at REPLServer.defaultEval (repl.js:132:27)
    at bound (domain.js:254:14)
    at REPLServer.runBound [as eval] (domain.js:267:12)
    at REPLServer.<anonymous> (repl.js:279:12)
    at REPLServer.emit (events.js:107:17)
    at REPLServer.Interface._onLine (readline.js:214:10)
    at REPLServer.Interface._line (readline.js:553:8)
    at REPLServer.Interface._ttyWrite (readline.js:830:14)
> 
(^C again to quit)
> 
$ nvm use node
Now using node v5.0.0
$ node
> Object.isExtensible(null)
false

[elicwhite]

Good catch. Added a test case for null.

[jhnns]

Shipped with 2.5.1