[c++] Dropping support for versions of Boost more than 2 years old

[chwarr]

In preparation for adding CI testing for Boost 1.66 (release December 18, 2017), we're thinking about dropping support for versions of Boost older than 2 years. This would mean that we only test with Boost 1.61 and above instead of the current 1.58 and above.

Over time, as functionality only available in later versions of Boost is used, Bond would stop building with older versions of Boost.

Please add a comment to this issue with your thoughts and concerns.

[jasonzio]

Significant changes to Boost Test in 1.56 make Boost 1.55 really sticky.

[chwarr]

Good point, @jasonzio. Thanks.

(And, we've had to do the Boost Test migration ourselves. :-))

One thing we're seeing in the opposite direction is the removal of things like std::auto_ptr from the standard library is pulling people up to Boost 1.65, the earliest version that excised its use of std::auto_ptr.