Add spec on Process.spawn with non-existing command.
Process.spawn with non-existing command sets $? accordingly.

Errors gotten from the pipe beetween the current process and the
forked one are now matched against Errno::NOENT.
A positive match means the launched command doesn't exist in
current PATH, thus $?'s pid and exit code must be set to the dead
process' and 127 respectively.
Fixed using previous gems configuration.
Adding spec for backreferences to keep matched string's class
Switched C-API to default to safe RSTRING.

If a C-ext modifies the RSTRING buffer, add the following:

  #define RSTRING_MODIFIED 1

to the appropriate header file or source file.

Since many performance issues related to C-exts are actually the RSTRING
caching code, we'd prefer to have C-exts break up front and fix them
than leave harder-to-find performance issues that mistakenly attribute
poor performance to Rubinius itself.
Added simple release task.
Added rubysl-digest dep for building with rbx.
Bumped version to 2.2.0.
Reset release date.
Updated CI specs to RubySpec c48d28a4.
Update CI tags.
Fix a spec typo for Exception#set_backtrace
Add Exception#set_backtrace specs for weird arguments
Fix Exception#set_backtrace for variety of arguments
Untag passing Exception#set_backtrace specs
Remove unused spec tags
Fix a sharing spec for Module#public with eval
Update Module#{module_function,private,protected,public} for eval
Untag passing Module#{module_function,private,protected,public} specs
Merge pull request #2785 from kachick/update_module-visibility_setters

Update Module#{module_function,private,protected,public} for eval