* New: cumulus/plugins.checks, plugin providing a oneDriver() function
to check that each net has one and only one driver. This is for
Cell that are not P&R (in which it is also checked). So, typically
the chip level.
* New: In cumulus/plugins.chip.core2chip, add a call to oneDriver().
* Bug: In cumulus/plugins.chip.core2chip, clear Spice extensions after
save. Otherwise we may use an outdated Spice extension after the
P&R. This is were Net missing Spice::Bit may occur.
Jean-Paul Chaput