Fix PkgVersion#<=>

Library/Homebrew/pkg_version.rb

@@ -30,6 +30,7 @@ class PkgVersion < Version
   alias_method :to_str, :to_s
 
   def <=>(other)
+    return unless Version === other
     super.nonzero? || revision <=> other.revision
   end
 end

Library/Homebrew/test/test_pkg_version.rb

@@ -24,6 +24,10 @@ class PkgVersionTests < Homebrew::TestCase
     assert_operator v("1.0_1"), :<, v("2.0_1")
     assert_operator v("HEAD"), :>, v("1.0")
     assert_operator v("1.0"), :<, v("HEAD")
+
+    v = PkgVersion.new("1.0", 0)
+    assert_nil v <=> Object.new
+    assert_raises(ArgumentError) { v > Object.new }
   end
 
   def test_to_s

Library/Homebrew/test/test_versions.rb

@@ -63,7 +63,9 @@ class VersionComparisonTests < Homebrew::TestCase
   end
 
   def test_comparison_returns_nil_for_non_version
-    assert_nil version('1.0') <=> 'foo'
+    v = version("1.0")
+    assert_nil v <=> Object.new
+    assert_raises(ArgumentError) { v > Object.new }
   end
 
   def test_compare_patchlevel_to_non_patchlevel