Implement rich RPM dependencies

This implements rich RPM dependencies, which are available with RPM
4.14+ (introduced in Fedora 27[1]). This means only a single line for a
dependency is used. That doesn't play well with the
.with_requires.commented_out approach that was implemented. This instead
moves the loop back to the template.

[1]: https://fedoraproject.org/wiki/Changes/RPM-4.14

lib/gem2rpm/rpm_dependency.rb

@@ -47,5 +47,11 @@ def to_rpm
       end
       rpm_dependencies.join("\n")
     end
+
+    # Returns string with entry suitable for RPM .spec file with RPM 4.14+.
+    def to_rich_rpm
+      rpm_dependencies = requirement.map { |v| v.to_s.empty? ? name : "#{name} #{v}" }
+      rpm_dependencies.size == 1 ? rpm_dependencies.first : "(#{rpm_dependencies.join(' with ')})"
+    end
   end
 end

templates/fedora-27-rawhide.spec.erb

@@ -22,9 +22,9 @@ BuildRequires: <%= requirement "ruby#{'-devel' unless spec.extensions.empty?}",
 # https://fedoraproject.org/wiki/Packaging:C_and_C++#BuildRequires_and_Requires
 BuildRequires: gcc
 <% end -%>
-<%= development_dependencies.reject do |d|
-  ["rdoc", "rake", "bundler"].include? d.name
-end.virtualize.with_requires.comment_out.to_rpm -%>
+<% for req in development_dependencies.reject { |d| ["rdoc", "rake", "bundler"].include? d.name }.virtualize -%>
+# BuildRequires: <%= req.to_rich_rpm %>
+<% end -%>
 <% if spec.extensions.empty? -%>
 BuildArch: noarch
 <% end -%>