Merge branch 'kn/refs-files-case-insensitive'

Deal more gracefully with directory / file conflicts when the files
backend is used for ref storage, by failing only the ones that are
involved in the conflict while allowing others.

* kn/refs-files-case-insensitive:
  refs/files: handle D/F conflicts during locking
  refs/files: handle F/D conflicts in case-insensitive FS
  refs/files: use correct error type when lock exists
  refs/files: catch conflicts on case-insensitive file-systems

refs.h

@@ -31,6 +31,8 @@ enum ref_transaction_error {
 	REF_TRANSACTION_ERROR_INVALID_NEW_VALUE = -6,
 	/* Expected ref to be symref, but is a regular ref */
 	REF_TRANSACTION_ERROR_EXPECTED_SYMREF = -7,
+	/* Cannot create ref due to case-insensitive filesystem */
+	REF_TRANSACTION_ERROR_CASE_CONFLICT = -8,
 };
 
 /*