[distcc] masquerade confusion

[Martin Pool]

I've just had a bit of confusion caused by ccache being installed as
cc on the path of a distccd instance.  distccd had been started as
root, and therefore ccache was trying to write to /root/.ccache, when
running as user distcc.  

>From the user's point of view the only message is something about
"ccache: /root/.ccache: permission denied", which is pretty confusing.

It would be nice if the failure were at least more obvious. 

Probably if that daemon had been a recent one, and if it had been
invoking distcc rather than ccache, then there would have been an
"inadvertent recursion" warning.

I'd like to improve this, if possible, before the next release.

-- 
Martin