RUBY-1273 Record guid on analytics events
RUBY-1273 Support referring txn GUID on analytics events
RUBY-1273 Only attach GUID with CAT

Java only generates GUID's when necessary. This helps save space on events in
analytics, since GUID's most transactions don't benefit from a GUID.

This commit makes sure we only use the TT GUID we generate for an event if:

1) We made a CAT call out
2) We're on the receiving end of CAT
3) RUM would include the GUID
RUBY-1273 Clearer cross-app conditionals
Merge pull request #389 from newrelic/RUBY-1273-dirac-guids

RUBY-1273 release attaching guid and referringTransactionGuid on events
Revert "Merge pull request #389 from newrelic/RUBY-1273-dirac-guids"

This reverts commit f6c656836154a8c31150e04a87630e68b30db952, reversing
changes made to da5c80687b86a8a26c615cdbf3a8b5b5355d2286.
Updating signing cert
CHANGELOG update for new certificate
Merge pull request #400 from newrelic/CHANGELOG_3.7.2_cert

CHANGELOG update for new certificate