Incompatibilities between spice3 and spice2

The output format of spice3 is slightly different for .print and .plot lines.
Most notably, different traces on plots are not scaled independently.  This
is most noticeable on phase/magnitude plots from an AC analysis (also,
phase is displayed in radians).  Finally, frequency for ".PRINT AC" lines
is displayed as a complex quantity with an all-zero imaginary component.

For input, "POLY( )" sources are not supported (the non-linear dependent
source provides a more general replacement).  Also, the ".ALTER" line
is not supported.  The Spice3 parser may be slightly different
on subtle points of reading input (lines need not start at column 1
for instance).