Merge branch 'jk/info-alternates-fix' into maint

A regression fix for 2.11 that made the code to read the list of
alternate object stores overrun the end of the string.

* jk/info-alternates-fix:
read_info_alternates: warn on non-trivial errors
read_info_alternates: read contents into strbuf

diff --cc sha1_file.c
Simple merge