Adding or modifying any map repo makes all repos non-upgradable

[Joshua Judson Rosen]

All of the map repositories are currently defined together in a single GConf value, which means that customising *any* repository-definition requires freezing *all* repository-definitions into the user-set value. This means that it's not possible to just modify some subset of the repositories' definitions (or even add one, or remove or deactivate one) and have the other definitions remain in a true `default' state where they'd be defined as `whatever default values are supplied by the GConf schema'.

This basically means that, if the user has modified any repository-definition in any way, then no repository-definitions can be automatically upgraded anymore—not even other repositories that the user didn't touch.

cf. bug #846485, which is impacted by this issue.

[Joshua Judson Rosen (rozzin)]

It seems like the right way to handle this is probably to give each repo its own GConf subtree (with separate keys for name, URL, etc.), and possibly include a `map_repos' list in GConf which simply indicates which repos are actually used their ordering.