Fix #8446.

Provides a universal default action (ignore) when a key cannot be found in the
keymap.
Merge pull request #8462 from blakejohnson/default-ignore

Fix #8446.
Add documentation on FFTW threads (relevant to #8455).
Merge branch 'master' of github.com:JuliaLang/julia
Makefile cleanups
Append to LDFLAGS even if set in environment
Merge branch 'upstream-master' into memdebug