GH #504: Infinite loop (or performance issue) writing using MultiByteEncoding (O(n^2) -> O(n))
Add -ea to Rake test runs and fix some asserted paths.
Top-level "sh" is no longer in Rake 10+; just use system.
Incorporate Krypt and wire it up for OpenSSL::PKCS5.
Implement OpenSSL digest block_length (in part, at least).
Remove assertions on instance var name.

I have run into two cases today where we are too strict about
instance variable names.

The first case I ran into was in Psych's accessing
internal instance variables with private_iv_get. We used
getInstanceVariable which attempts to enforce that all incoming
var names are valid instance variables. MRI does not enforce this
for C-level instance variable lookups, apparently.

The second is in krypt, accessing internal variables for similar
reasons.

Because of these two cases, and because we *know* there's
variables in the table with non-standard names, I'm removing the
assertions.

This allows JRuby + krypt to pass tests as before, even with
assertions turned on.
Inherit the same "thread" in a fiber as the parent. Fix JRUBY-7081
[IR] Further tweaking of interpreter loop.

* Increment ipc always in the loop -- DRYs out interp loop further.
* Minor to noticeable speedup on several benchmarks.
'install-jruby-launcher-gem' target requires 'rake'.