Insert $(DESTDIR) in "rm -f" commands in src/Makefile.in::install-exec-local.
This fixes abuild failure when a version of the package is already
installed.

Not bumping PKGREVISION because the resulting package should be unchanged.
Add dependency on py-lxml, used by xenapi_create.py.
Dependency reported missing by Kamil Rytarowski <n54@gmx.com> on
pkgsrc-users.

Bump PKGREVISION.
Updated sysutils/xentools42 to 4.2.4nb1