#19 tstep = 0 or not set should be accepted

[marcel hendrix]

I found it a nuisance to have to set tstep=x for the .tran
command. Setting a too small value for tstep slows down the
simulation unnecessarily.

Exeprimenting with tstep, I found that TRANfinalTime is 0 when
the tend parameter of .tran is parameterized like .tran {t_end}.
At least, TRANfinalTime is 0 during TRANsetParm().

I've appended a changed transetp.c file in the hope it will be useful.

-marcel