SI-4760 Parser handles block-ending import

Don't molest the RBRACE.

Updated with additional parse tests suggested
by @retronym.  "What are you lazy?"  Yes, I
must be lazy.  Can't ScalaCheck or Par-Test
generate these tests automatically?  That seems
like a reasonable expectation.
Merge pull request #2899 from som-snytt/issue/4760-parser

SI-4760 Parser handles block-ending import