RUBY-1123 Fix Sequel instrumentation for older versions

Checks for versions older than 3.37.0, which is the version which
the extensions and plugins system API was added in its current form.

Logs a message for older versions.
RUBY-1123 Fix the minimum version number in the log message.
RUBY-1123 Add links to the issue and ticket to the multiverse test for reference
RUBY-1123 Guard against Sequel::MAJOR being undefined

Sequel::MAJOR was added in 2.10.0, so add that to the multiverse
tests and guard against it being undefined. (props to Ben for
spotting this)
RUBY-1123 No 1.9 Hash syntax for you!
RUBY-1123 Specify paths to newrelic_rpm so that they will work in CI
RUBY-1123 Make Sequel multiverse test work on JRuby