out of tree build fixes

[David Bremner]

Apparently we've neglected the out of tree builds even more than
usual. I originally thought this is what was causing the test failures
on buildbot. I'm less sure now, but I think these fixes don't hurt
anything, and they do unbreak out of tree builds for me.

There is certainly still work to be done with our out of tree builds.
For those of you just joining the party, that doesn't mean we want to
switch to your favourite build system. Or even to Autotools.

An earlier draft of this series (discussed on IRC) defined a builddir
variable, but eventually I realized the current directory of make is
always builddir. So at least for now that doesn't seem to be needed.