Add Process.setproctitle().

* ruby.c (Process.setproctitle): New method to change the title of
  the running process that is shown in ps(1). [Feature #8696]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42425 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Add Process.argv0.

* ruby.c (Process.argv0): New method to return the original value
  of $0. [Feature #8696]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42426 b2dd03c8-39d4-4d8f-98ff-823fe69b080e