For some reason git shortlog spits out non-breaking spaces, let's remove
that, as for our purposes (inclusion in NEWS) we really want breaking
(i.e. normal) spaces.
Shell scripts should be executable so that meson reports their
invocation succinctly (does not print 'sh' '-e').
Python scripts should not be executable so that meson does the
detection of the right python binary itself.
Add -u everywhere to catch potential errors.