branchmap: remove extra indent This clean up the rest of the previous changeset.

branchmap: simplify error handlind when writing rev branch cache Now that we have a general try except, we can move the error handling from the individual writes in it. Code will be reindented in the next changeset to help this on readability.

branchmap: acquires lock before writting the rev branch cache We now attempt to acquire a lock and write the branch cache within that lock. This would prevent cache corruption when multiple processes try to write the cache at the same time.

branchmap: preparatory indent of indent the branch rev writing code The rev branch cache is written without a lock, we are going to fix this but we indent the code beforehand to make the next changeset clearer.