This is actually the third time I fix random_graph().  On
2007-02-06 I changed the function not to generated dead states,
but in a way that made it non-deterministic.  On 2010-01-20 I made
the function deterministic again, but it started to generate dead
states as a side effect.  This time, I'm making sure that dead
states won't come again with a test-case that we should have had
from the beginning.

* src/tgbaalgos/randomgraph.cc (random_graph): Add an extra
indirection array, state_randomizer[], so that we can reorder
states indices after a random selection without actually changing
the value of the indices used by unreachable_states and
nodes_to_process.
* src/tgbatest/randtgba.test: New file.
* src/tgbatest/Makefile.am: Add randtgba.test.