Merge branch 'rs/refs-string-slice'

Avoid unnecessary temporary allocations while looking for matching refs
inside refs API.

By René Scharfe (3) and Junio C Hamano (1)
* rs/refs-string-slice:
refs: do not create ref_entry when searching
refs: use strings directly in find_containing_dir()
refs: convert parameter of create_dir_entry() to length-limited string
refs: convert parameter of search_ref_dir() to length-limited string

diff --cc refs.c
Simple merge