./run: Set s= (srcdir).  Use absolute paths.
perl: run-bindtests: Don't set PERL5LIB.

This environment variable should already be set properly
by 'run', there is no need to set it from this test script.
perl: Fix build and test to work with separated builds.

This is inspired largely by Hilko Bengen's equivalent
hivex patch here:

https://github.com/libguestfs/hivex/commit/887466794a40f57b84ce32524e1a650d6674c7e6
python: Fix for separated builds.

Ensure that ./run sets PYTHONPATH to include the Python source
directory (location of guestfs.py).
erlang: Add a CLEANFILES rule.
erlang: Make separated builds work correctly.

Set ERL_LIBS and also create a phony 'ebin' directory for the
guestfs.beam (library) so that the tests run against the local copy
not the installed version, and so that separated builds work.