Introduce `Rails.gem_version`

This method return `Gem::Version.new(Rails.version)`, suggesting a more
reliable way to perform version comparison.

Example:

    Rails.version #=> "4.1.2"
    Rails.gem_version #=> #<Gem::Version "4.1.2">

    Rails.version > "4.1.10" #=> false
    Rails.gem_version > Gem::Version.new("4.1.10") #=> true
    Gem::Requirement.new("~> 4.1.2") =~ Rails.gem_version #=> true

This was originally introduced as `.version` by @charliesome in #8501
but got reverted in #10002 since it was not backward compatible.

Also, updating template for `rake update_versions`.

1 files changed, 1 insertions, 1 deletions

diff --git a/Rakefile b/Rakefile
index fadebc241f..5585280589 100644
--- a/Rakefile
+++ b/Rakefile
@@ -66,7 +66,7 @@ task :update_versions do
   version_file = File.read("version.rb")
 
   PROJECTS.each do |project|
-    Dir["#{project}/lib/*/version.rb"].each do |file|
+    Dir["#{project}/lib/*/gem_version.rb"].each do |file|
       File.open(file, "w") do |f|
         f.write version_file.gsub(/Rails/, constants[project])
       end