Treat relative paths as relative to parent project's remote (#522)

* Treat relative paths as relative to parent project's remote

* replace unit test case with integration test

* run relative URL test only on supported CMake versions (3.27)

* omit cmake 2.25.x test runner as replaced by 2.27.x

---------

Co-authored-by: Chris Wright <chris.wright@mqa.co.uk>
Co-authored-by: Lars Melchior <lars.melchior@gmail.com>

test/integration/test_relative_urls.rb

@@ -0,0 +1,17 @@
+require_relative './lib'
+
+class RelativeURLs < IntegrationTest
+  def setup
+    # relative URLs were introduced in CMake 3.27
+    @relative_urls_supported = (!ENV['CMAKE_VERSION']) || (Gem::Version.new(ENV['CMAKE_VERSION']) >= Gem::Version.new('3.27'))
+  end
+
+  def test_add_project_with_relative_urls
+    omit_if !@relative_urls_supported do
+      prj = make_project from_template: 'using-fibadder'
+      prj.create_lists_from_default_template package: 'CPMAddPackage("gh:cpm-cmake/testpack-fibadder@1.1.0-relative-urls")'
+      assert_success prj.configure
+      assert_success prj.build
+    end
+  end
+end