Return a 404 rather than an error page if the key cannot be found.

src/keas/kmi/README.txt

@@ -251,6 +251,21 @@ encryption key string:
   >>> len(encKey)
   32
 
+If you try to request a nonexistent key, you get a 404 error:
+encryption key string:
+
+  >>> import cStringIO
+  >>> io = cStringIO.StringIO('xyzzy')
+
+  >>> request = TestRequest(io)
+  >>> request.method = 'POST'
+
+  >>> keyCall = rest.KeyView(keys, request)
+  >>> print keyCall()
+  Key not found
+  >>> request.response.getStatus()
+  404
+
 A `GET` request to the root shows us a server status page
 
   >>> request = TestRequest()

src/keas/kmi/rest.py

@@ -45,4 +45,9 @@ def POST(self):
         stream.seek(0)
         key = stream.read()
         self.request.response.setHeader('content-type', 'text/plain')
-        return self.context.getEncryptionKey(key)
+        try:
+            return self.context.getEncryptionKey(key)
+        except KeyError:
+            self.request.response.setStatus(404)
+            return 'Key not found'
+