pcp

Replace xconfirm with pmconfirm from pcp-gui.

There's pretty much no situation where we want to use
xconfirm anymore - it looks tragic on current X11 (no
theme/desktop integration), and doesn't exist on the
other platforms (Mac/Win). The configuration option
remains in pcp.conf, however - several tools use this
and its arguably part of the API now - so it remains.

Also snuck a pmdalinux makefile cleanup - no longer
need to link with libpthread.