Stop stopping writes on bg_error_

Summary: This might have caused https://github.com/facebook/rocksdb/issues/345. If we're stopping writes and bg_error comes along, we will never unblock the write.

Test Plan: compiles

Reviewers: ljin

Reviewed By: ljin

Subscribers: leveldb

Differential Revision: https://reviews.facebook.net/D24807
Options correction
Merge pull request #352 from fyrz/OptionsTestMergeProblem

Options correction related to merge