merge revision(s) 43609,43617: [Backport #8878] [Backport #9085]

	vcs.rb: split

	* tool/vcs.rb: split from file2lastrev.rb.
	* tool/rbinstall.rb (Gem::Specification.load): obtain spec date from
	  VCS for the case using git, RUBY_RELEASE_DATE is the last resort.
	  probably fixes [Bug #9085].


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@43655 b2dd03c8-39d4-4d8f-98ff-823fe69b080e