Ruby 2.6.0 development has started.

Fix rbenv install on Solaris / Illumos

rbenv install crashes on Solaris with an empty log file. Adding support
for the proper Solaris getconf call in num_cpu_cores fixed it. Tested
and working under OmniOS CE r151024.

Add 2.4.3, 2.3.6, 2.2.9, and 2.5.0-rc1

Upgrade to OpenSSL 1.0.2n

Add JRuby 9.1.15.0

Relax java version regexp

num_cpu_cores: Prefer getconf over cpuinfo grep, simplify grep usage

Add definition for JRuby 9.1.14.0

## Summary

JRuby 9.1.14.0 has been released.
http://jruby.org/2017/11/08/jruby-9-1-14-0.html

## Other Information

JRuby 9.1.14.0+ download URL has changed.
https://github.com/rbenv/ruby-build/issues/1148

Fix OpenSSL version

Upgrade to OpenSSL 1.0.2m and 1.1.0g

Added 2.5.0-preview1 definition

This allows the java version to be specified as "9", instead of "1.9".

Closes #1135

Add rbx-3.83 and rbx-3.84

`--quiet` option isn't sensible sha256sum(1) of GNU coreutils

The option is available only if verifying digest, not available when computing digest.

>       --quiet
>              don't print OK for each successfully verified file

Quote JRuby check on FreeBSD to avoid "unary operator" syntax issue.

Ignore everything after whitespace in the output from sha256sum