Merge branch 'jk/reading-packed-refs'

An earlier rewrite to use strbuf_getwholeline() instead of fgets(3)
to read packed-refs file revealed that the former is unacceptably
inefficient.

* jk/reading-packed-refs:
t1430: add another refs-escape test
read_packed_refs: avoid double-checking sane refs
strbuf_getwholeline: use getdelim if it is available
strbuf_getwholeline: avoid calling strbuf_grow
strbuf_addch: avoid calling strbuf_grow
config: use getc_unlocked when reading from file
strbuf_getwholeline: use getc_unlocked
git-compat-util: add fallbacks for unlocked stdio
strbuf_getwholeline: use getc macro

diff --cc config.c
Simple merge

diff --cc refs.c
Simple merge