add test verifying that views do not index design docs

Added a new test verifying that views don't index design documents. This
test reveals a bug in the current master branch of
couchbase/couchbase-lite-java-core (99a9e8b6ba), where updateIndex() will
crash if the last document to index is a design doc. I could have tested
the crash condition directly, but I thought this test would be more
meaningfulr/useful.
Merge pull request #275 from mjq/index_crash

Add test verifying that views do not index design docs