yume todo authored Apr 06, 2017 and Brad King committed Apr 06, 2017

Changes in commit 3ca6f70f (FindBoost: Allow testing for multiple
compiler suffixes, 2017-03-28) accidentally left a `set()` instead of a
`list(APPEND)` while constructing `_boost_RELEASE_NAMES`.  Fix the logic
to match what was done for `_boost_DEBUG_NAMES`.  Otherwise we drop some
of the candidate names.