Merge branch 'mh/strbuf-read-file-returns-ssize-t'

Avoid possible ssize_t to int truncation.

* mh/strbuf-read-file-returns-ssize-t:
strbuf: strbuf_read_file() should return ssize_t

diff --cc strbuf.c
Simple merge

diff --cc strbuf.h
Simple merge