inheritable annex.securehashesonly

* init: When annex.securehashesonly has been set with git-annex config,
  copy that value to the annex.securehashesonly git config.
* config --set: As well as setting value in git-annex branch,
  set local gitconfig. This is needed especially for
  annex.securehashesonly, which is read only from local gitconfig and not
  the git-annex branch.

doc/todo/sha1_collision_embedding_in_git-annex_keys.mdwn has the
rationalle for doing it this way. There's no perfect solution; this
seems to be the least-bad one.

This commit was supported by the NSF-funded DataLad project.

Command/Config.hs

@@ -9,6 +9,7 @@ module Command.Config where
 
 import Command
 import Logs.Config
+import Config
 
 cmd :: Command
 cmd = noMessages $ command "config" SectionSetup
@@ -52,12 +53,14 @@ seek (SetConfig name val) = commandAction $ do
 	showStart name val
 	next $ next $ do
 		setGlobalConfig name val
+		setConfig (ConfigKey name) val
 		return True
 seek (UnsetConfig name) = commandAction $ do
 	allowMessages
 	showStart name "unset"
 	next $ next $ do
 		unsetGlobalConfig name
+		unsetConfig (ConfigKey name)
 		return True
 seek (GetConfig name) = commandAction $ do
 	mv <- getGlobalConfig name