This purely textual change is in preparation for storing references
hierarchically, when the old ref_array structure will represent one
"directory" of references. Rename functions that deal with this
structure analogously, and also rename the structure's "refs" member
to "entries".
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>