Add unit tests covering closure and close() throwing.
Assert that close()'s exception is not always suppressed.

See JDK7's try-with-resources [1] for justification, where the close()
exception is propogated if the body returns normally.

[1] http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.20.3
Upgrade sbt version and tweak mima settings for 2.10
Merge remote-tracking branch 'blair/add-exception-throwing-assertions' into fix/issue-18
Fixed issue with exceptions on close *not* causing an error to be thrown.
This behavior should perhaps be configurable, but for now it's better to return the exception.  Maybe
in the future we try to return the value we had before the close exception as well.

For now, let's just mimic Java, and tweak when we can.
Merge pull request #22 from jsuereth/fix/issue-18

Fix/issue 18