Adding transient simulation top generate the operating point of a circuit

The operating point of a circuit has to be established before a transient, ac, 
or noise simulation may be started.

The procedure, as found in cktop.c is as follows:
1) Iterate the matrix with the starting values
If this fails:
2) Start gmin stepping
If this fails:
3) start source stepping

If this again fails, bail out.

In this branch a fourth method is added:
4) Start a transient simulation for a specific amount of time.
   Keep all data local. Keep the matrix values as an
   operating point for the simulation that is following.
If this fails, finally stop.

A new command sets the flags for transient op calculation
optran n1 n2 n3 n4 n5 n6
This command has to be given before the simulation commands
run, ac, tran, pz, or noise. Only the simulation commands will
start the (modified) op calculation. Another 'optran' will
override the previous flags.

Step 1 (from above) may be skipped by
option noopiter
command optran n1 overrides noopiter

Step 2 may be skipped by
option gminsteps=0
command optran n2 overrides gminsteps

Step 3 may be skipped by 
option srcsteps=0
command optran n3 overrides srcsteps

n4 sets the step size for transient simulation towards the operating point.

n5 sets the time for transient simulation towards the operating point.

n6 set a ramp time to ramp all independent voltage or
current sources until 100% is reached at opramptime.

The transient op calculation uses the 'UIC' flag for its startup.
Basically two applications come to mind: You may use this with
constant voltage and current sources and simulate until the 
output is stable. A method to automatically stop the op transient
simulation when all nodes have become stable, might be desirable,
but has not yet been implemented.
One also may use the optran for a first transient simulation, maybe
with different step sizes, before the next (tran, ac, pz, noise)
simulation is commencing. So you may reach a certain bias point
quickly and with coarse time steps, and then continue with fine
steps to see details. For example a power amp in electro-thermal
simulation may run for some seconds (minutes?) until the final
temperature is reached, and then the detailed transient or
an ac simulation starts.