Add a function for inserting a C string into a strbuf. Use it
throughout the source to get rid of magic string length constants and
explicit strlen() calls.
Like strbuf_addstr(), implement it as an inline function to avoid the
implicit strlen() calls to cause runtime overhead.
Helped-by: Taylor Blau <me@ttaylorr.com> Helped-by: Eric Sunshine <sunshine@sunshineco.com> Signed-off-by: René Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>