[PATCH] add a reflog_exists and delete_reflog abstraction

This is a single patch that adds two new functions to try to hide the reflog implementation details from the callers in checkout.c and reflog.c. It adds new functions to test if a reflog exists and to delete it, thus allowing checkout.c to perform this if-test-then-delete operation without having to know the internal implementation of reflogs (i.e. that they are files that live unde r.git/logs)

It also changes checkout.c to use ref_exists when checking for whether a ref exists or not instead of checking if the loose ref file exists or not. Using ref_exists instead both hides the reflog implementation details from checkout.c as well as making the code more robust against future changes. It currently has a hard assumption that the loose ref file must exist at this stage or else it would end up deleting the reflog which is true today, as far as I can tell, but would break if git would change such that we could have a branch checked out without having a loose ref file for that branch.

Ronnie Sahlberg (1):
  refs.c: add new functions reflog_exists and delete_reflog

 builtin/checkout.c |  8 ++------
 builtin/reflog.c   |  2 +-
 refs.c             | 20 ++++++++++++++------
 refs.h             |  6 ++++++
 4 files changed, 23 insertions(+), 13 deletions(-)