Implement XSVF support for detailed state path transitions,
by collecting sequences of XSTATE transitions into paths
and then calling pathmove().

It seems that the Xilinx tools want to force state-by-state
transitions instead of relying on the standardized SVF paths.
Like maybe there are XSVF tools not implementing SVF paths,
which are all that we support using svf_statemove().

So from IRPAUSE, instead of just issuing "XSTATE DRPAUSE"
they will issue XSTATES for each intermediate state: first
IREXIT2, then IRUPDATE, DRSELECT, DRCAPTURE, DREXIT1, and
finally DRPAUSE.  This works now.

Handling of paths that go *through* reset is a trifle dodgey,
but it should be safe.

Tested-by: Wookey <wookey@wookware.org>

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>