Updated the 'crypto++' package to use an improved URL formation scheme (inspired by changes made to the 'Silo' package).

var/spack/repos/builtin/packages/cryptopp/package.py

@@ -8,8 +8,8 @@ class Cryptopp(Package):
        public-key encryption (RSA, DSA), and a few obsolete/historical encryption
        algorithms (MD5, Panama)."""
 
-    homepage = "http://www.cryptopp.com/"
-    url      = "http://www.cryptopp.com/cryptopp563.zip"
+    homepage = "http://www.cryptopp.com"
+    base_url = "http://www.cryptopp.com"
 
     version('5.6.3', '3c5b70e2ec98b7a24988734446242d07')
     version('5.6.2', '7ed022585698df48e65ce9218f6c6a67')
@@ -28,4 +28,4 @@ def url_for_version(self, version):
         version_tuple = tuple(v for v in iter(version))
         version_string = reduce(lambda vs, nv: vs + str(nv), version_tuple, "")
 
-        return "%scryptopp%s.zip" % (Cryptopp.homepage, version_string)
+        return '%s/cryptopp%s.zip' % (Cryptopp.base_url, version_string)