Reimplementation of code to allow bounded request queues - rejecting requests when the queue is full. Fixes #1301.

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branch : 1301-reject-conns-when-full
Merge fix for #1301 (reject connections when queue is full).
Adding a changelog to capture high level changes.
Bumped to 3.5.0 in preparation for next release.
Added tag 3.5.0 for changeset fd745f2e7c44
Bumped to 3.5.1 in preparation for next release.