Update concretize to check for more changes and iterate further.

var/spack/mock_packages/optional-dep-test-3/package.py

@@ -0,0 +1,17 @@
+from spack import *
+
+class OptionalDepTest3(Package):
+    """Depends on the optional-dep-test package"""
+
+    homepage = "http://www.example.com"
+    url      = "http://www.example.com/optional-dep-test-3-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    variant('var', default=False)
+
+    depends_on('a', when='~var')
+    depends_on('b', when='+var')
+
+    def install(self, spec, prefix):
+        pass