branchcache: move the processing of the new data in a dedicated method
In a future changeset, this will allow the V3 of the branch cache to use a fast
path when possible.
# Tests to be disabled when building and testing in the Nix sandbox.
# tests enforcing "/usr/bin/env" shebangs, which are patched for nix
test-run-tests.t
test-check-shbang.t
# doesn't like the extra setlocale warnings emitted by the nix bash wrappers
test-locale.t