add fry-hstore.gemspec
add an explicit source to Gemfile
assign @fallback via lvariable 'fallback'.
extend HStore#method_missing spec.
Revert "assign @fallback via lvariable 'fallback'."

This reverts commit 0546b519598d4d49dbd4d1a3628d52efa9b34dcb.
remove code that depends on Fry.inspect()