We can remove those C++11 and C++14 kludges because we require GCC 4.9
now.

Fixes build failure on OS X, closes #44.  With the other plugins,
that's not critical, because those use the AudioOutputWrapper, which
hides this problem.

See commit 71f0ed8b

See commit 788e3b31 for an explanation.

release v0.20.7

Closes #34