Fix crash in src/errors.js, see https://github.com/mozilla/makedrive/issues/145
Merge pull request #244 from humphd/better-errors

Fix crash in src/errors.js, see https://github.com/mozilla/makedrive/issues/145
Fix #247 - sh.cwd() not updating cwd on success, with test.
Deal with all other uses of this.cwd etc and convert to pwd() on current shell instance.
Merge pull request #248 from humphd/issue247

Fix #247 - sh.cwd() not updating cwd on success, with test.
v0.0.21