Added ability to set a temp directory

For Windows, temp directories must be in the same drive as the files to be browserified, without which the karma-browserifast cannot work.

I'm not sure why exactly and I am not able to debug this (I'm on Mac). A workaround is to have the developer set a tmpDir in framework.browserify options. This fixes the issue in Windows if you specify a tmpDir that is 'tmp'. I added mkdirp to create this directory if it is not present.

Example usage:
```
		browserify: {
			tmpDir: 'tmp',
			files: [
				'test/classes/units/*.js'
			]
		},

```

If tmpDir is not specified the OS's tmp dir is used as per the original implementation.

Thanks.