bugreport: add tool to generate debugging info

Teach Git how to prompt the user for a good bug report: reproduction
steps, expected behavior, and actual behavior. Later, Git can learn how
to collect some diagnostic information from the repository.

If users can send us a well-written bug report which contains diagnostic
information we would otherwise need to ask the user for, we can reduce
the number of question-and-answer round trips between the reporter and
the Git contributor.

Users may also wish to send a report like this to their local "Git
expert" if they have put their repository into a state they are confused
by.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.c

@@ -539,6 +539,10 @@ ssize_t strbuf_write(struct strbuf *sb, FILE *f)
 	return sb->len ? fwrite(sb->buf, 1, sb->len, f) : 0;
 }
 
+ssize_t strbuf_write_fd(struct strbuf *sb, int fd)
+{
+	return sb->len ? write(fd, sb->buf, sb->len) : 0;
+}
 
 #define STRBUF_MAXLINK (2*PATH_MAX)