localrepo: introduce shared method to check if a repository is shared
Up until now we compared the "path" and "sharedpath" repository properties to
check if a repository is shared. This was relying an implementation detail of
shared repositories. In order to make it possible to change the way shared
repositories are implemented, we encapsulate this check into its own localrepo
method, called shared.
This new method returns None if the repository is shared, and something else
(for now a string describing the short of share) otherwise.
The reason why I did not call this method "isshared" and made it return a
boolean is that I plan to introduce a new type of shared repository soon.
# NOTES:
This is the first patch in a series whose purpose is to add support for
creating "full repository shares", which are repositories that share everything
with the repository source except their current revision, branch and bookmark.
This series is RFC because I am not very sure of some of the solutions I took.
Comments are welcome!