be stricter about rejecting invalid configurations for remotes

This is a first step toward that goal, using the ProposedAccepted type
in RemoteConfig lets initremote/enableremote reject bad parameters that
were passed in a remote's configuration, while avoiding enableremote
rejecting bad parameters that have already been stored in remote.log

This does not eliminate every place where a remote config is parsed and a
default value is used if the parse false. But, I did fix several
things that expected foo=yes/no and so confusingly accepted foo=true but
treated it like foo=no. There are still some fields that are parsed with
yesNo but not not checked when initializing a remote, and there are other
fields that are parsed in other ways and not checked when initializing a
remote.

This also lays groundwork for rejecting unknown/typoed config keys.

Assistant/WebApp/Configurators/WebDAV.hs

@@ -22,6 +22,7 @@ import Git.Types (RemoteName)
 import Assistant.Gpg
 import Types.GitConfig
 import Annex.SpecialRemote.Config
+import Types.ProposedAccepted
 
 import qualified Data.Map as M
 #endif
@@ -58,7 +59,7 @@ postEnableWebDAVR uuid = do
 	m <- liftAnnex readRemoteLog
 	let c = fromJust $ M.lookup uuid m
 	let name = fromJust $ lookupName c
-	let url = fromJust $ M.lookup "url" c
+	let url = fromProposedAccepted $ fromJust $ M.lookup (Accepted "url") c
 	mcreds <- liftAnnex $ do
 		dummycfg <- liftIO dummyRemoteGitConfig
 		getRemoteCredPairFor "webdav" c dummycfg (WebDAV.davCreds uuid)