Deprecation warnings in latest SASS

Latest SASS (v3.3.0.rc.2) shows the following deprecation warnings when compiling. I think my changes fix this.

```
DEPRECATION WARNING on line 187 of components/foundation/scss/foundation/components/_global.scss:
Assigning to global variable "$default-float" by default is deprecated.
In future versions of Sass, this will create a new local variable.
If you want to assign to the global variable, use "$default-float: left !global" instead.


DEPRECATION WARNING on line 188 of components/foundation/scss/foundation/components/_global.scss:
Assigning to global variable "$opposite-direction" by default is deprecated.
In future versions of Sass, this will create a new local variable.
If you want to assign to the global variable, use "$opposite-direction: right !global" instead.


DEPRECATION WARNING on line 9 of components/foundation/scss/foundation/components/../_functions.scss:
Assigning to global variable "$modules" by default is deprecated.
In future versions of Sass, this will create a new local variable.
If you want to assign to the global variable, use "$modules: append($modules, $name) !global" instead.
```