Move `helm-fuzzy-matching-default-sort-fn-1' logic into `helm-fuzzy-sort-fn'.

- `helm-M-x' was referencing the internal implementation, which makes it
  awkward to override with a custom sorter.
Minor fixes in previous (#783 PR) commit.

* helm-command.el (helm-M-x): source arg in sort fn is in use there.
* helm.el (helm-fuzzy-matching-default-sort-fn): Reindent.