Prefer Class.base() over goog.base()

`goog.base` is not compatible in es5 strict mode.  A replacement is available in the form of a base method added to constructors by `goog.inherit`.

The syntax is slightly different when calling from a constructor, so it is best to give an example:

Example before:

    /** @constructor @extends {B} */
    function C() {
      goog.base(this);
    }
    goog.inherit(C, B);

    C.prototype.method = function() {
      goog.base(this, 'method');
    }

Example after:

    /** @constructor @extends {B} */
    function C() {
      C.base(this, 'constructor');
    }
    goog.inherit(C, B);

    C.prototype.method = function() {
      C.base(this, 'method');
    }

Both `goog.base` and `C.base` are rewritten by the compiler when optimizations are enabled, so there are no differences in the resulting output. Please note however that `goog.base(this, 'constructor')` is **not** valid.
Merge pull request #8 from jart/patch-4

Prefer Class.base() over goog.base()