First part of the format-upgrade support in repo

 In order to work across major bumps, we need to add a call to
s6-rc-format-upgrade before s6-rc-update in the s6-rc-set-install
sequence of commands.
 s6-rc-format-upgrade only works when the db is exactly the same
across s6-rc versions. That means we need to have the source version
of the current live set at all times, in order to compile it with
the new s6-rc version before upgrading and then updating.
 So:
 1. we take a snapshot of the source version of a set every time
we commit.
 2. we refuse to install if we don't have the snapshot.
 3. we add s6-rc-format-upgrade to the processing chain
 4. for cleanup: after installing, we delete all the snapshots of
the set except the one that corresponds to the newly
installed live set.

 This commit implements 1: taking the snapshot. It's a regular
s6-rc-set-copy, using an internal name. We refactor
s6-rc-set-copy and s6-rc-set-delete to have primitives we can
use internally.

 Wait for later commits before using repo, else you'll fill
your repository with snapshots that won't get cleaned up.

 TBD: how to store the s6-rc version in the compiled db. We
probably need to add a small file in there.

1 files changed, 2 insertions, 0 deletions

diff --git a/src/repo/deps-lib/s6rcrepo b/src/repo/deps-lib/s6rcrepo
index 7d8b816..1935001 100644
--- a/src/repo/deps-lib/s6rcrepo
+++ b/src/repo/deps-lib/s6rcrepo
@@ -26,6 +26,8 @@ s6rc_repo_rxnames.o
 s6rc_repo_sanitize_setname.o
 s6rc_repo_sanitize_svname.o
 s6rc_repo_setcompile.o
+s6rc_repo_setcopy.o
+s6rc_repo_setdelete.o
 s6rc_repo_setuptodate.o
 s6rc_repo_sv_bcmpr.o
 s6rc_repo_sv_cmpr.o