Add better error reporting for port declarations.
Add better error reporting for port declarations.

Add an error message for NULL port declarations and for a ';'
that could be left over from building a port declaration from
an old style declaration.

themperek/iverilog,CastMi/iverilog,themperek/iverilog,CastMi/iverilog,themperek/iverilog,CastMi/iverilog