rollback stack before executing ensure clause.
catching NameError here is not desirable.
Minor code format changes.
Fix typo.
Merge pull request #1184 from iij/pr-ensure-on-correct-stack

Rollback stack before executing ensure clause.
Merge pull request #1186 from carsonmcdonald/mrbcfixup

Minor format changes and a typo fix
Merge branch 'master' into iij