ruby: Use updated package names, but allow fallback to the old names (RHBZ#894545).

Thanks Dominic Cleal.

ruby/Rakefile.in

@@ -17,9 +17,24 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
 require 'rake/clean'
-require 'rake/rdoctask'
 require 'rake/testtask'
-require 'rake/gempackagetask'
+
+# Used to be rake/rdoctask.  Now it's rdoc/task.
+begin
+  require 'rdoc/task'
+rescue
+  require 'rake/rdoctask'
+end
+
+# Used to be rake/gempackagetask.  Now it's rubygems/package_task.  Also
+# we need to use the appropriate class name below.
+begin
+  require 'rubygems/package_task'
+  gempackagetask='Gem::PackageTask'
+rescue
+  require 'rake/gempackagetask'
+  gempackagetask='Rake::GemPackageTask'
+end
 
 PKG_NAME='@PACKAGE_NAME@'
 PKG_VERSION='@PACKAGE_VERSION@'
@@ -108,7 +123,7 @@ Ruby bindings for libguestfs.
 EOF
 end
 
-Rake::GemPackageTask.new(SPEC) do |pkg|
+eval(gempackagetask).new(SPEC) do |pkg|
     pkg.need_tar = true
     pkg.need_zip = true
 end