Works around Rubinius bug
Uses string messages for errors
rbx build is green; let us try to keep it that way
Revert "rbx build is green; let us try to keep it that way"

This reverts commit aa473cdf4651f7530f44ea0e905e8e230f4e0e35.
Merge branch 'change-be-true-false-to-truthy-falsey' of https://github.com/samphippen/rspec-expectations into change-be-true-false-to-truthy-falsey
Alias be_falsy to be_falsey.

Signed-off-by: Sam Phippen <samphippen@googlemail.com>