Miscellaneous improvements in unit tests.

End statements with semicolons, to be consistent with the surrounding
code.

Added a new unit test to ensure environment variables are honored when
parsing a
connection string.

Added a TODO to cleanup a test that emits messages using console.log().

Correct a query's syntax. Looks like a good thing to do even though the
syntax
doesn't matter in mocked out tests.

Removed a test that tests for SELECT tags; AFAIK, SELECT commands don't
emit a
tag.
Update a test to pass.
Re-add the test for SELECT tag; I was wrong in my assumption.

Postgres generally does not emit a SELECT tag after a SELECT query, but
it does emit that tag after a CREATE TABLE x AS SELECT query.

Example:

postgres=# create table t as select 1;
SELECT 1
Merge pull request #608 from gurjeet/misc_unit_test_improvements

Miscellaneous improvements in unit tests.