ISSUE 1601: save/restore $! properly in the runtime

* Eliminates one more rubyspec error -- now down to to one
  failure before rubyspec run is green in IR mode.

* This also fixes the error with "bundle exec rake" with the
  gem "analytics-ruby" line in Gemfile in IR mode (reported
  by nirvdrum on IRC).

* This still requires another set of eyes going over all the
  files and see if other instances have been missed.