change save-some-buffers called when running mix command not to attempt to save buffers whose names starts with *.

This works around an issue when you try to run tests and have term or multi-term running. Before this change, it asked you to save every open term session.
merge with master
Merge pull request #8 from pragdave/change-save-buffers-predicate

change save-some-buffers called when running mix command not to attempt to save buffers whose names starts with *.