Fix various FTBFS reasons

Hi, I've seen too late how young the package upload was and now that I know I'm pretty sure you are on this anyway. But to help a bit here two fixes I've found today when looking at this package.

Fixes: "configure.ac:371: error: required file 'man/nbd-client.8.sh.in' not found" "/bin/sh: 1: git: not found"

Still remaining: "conftest.c:25:10: fatal error: ac_nonexistent.h: No such file or directory"

But this was when I realized the age, so I'll leave it to you at your own pace :-) Thanks in advance, Christian