Right, but if the user did "make install" they'd still hit the hg binary in
their home directory, so it makes sense for them to use the libraries in the
home directory. Of course, if they _want_ to use the global one and ditch the
local one, they could use a hypothetical "make uninstall-home" as before. If the
search path is "../lib/python", every hg binary would get the proper libraries.
However, I don't know enough about Linux distributions to know if that's safe in
the general case.

PYTHONPATH works for the libraries, but not the main binary.