This corrects an error that caused SIO reject when SIO occured before
a pending seek interrupt on a different device.
- Move the interrupt pending test from sigma_io.c into each device.
- Make the sigma_dp.c test a special case that looks for pending
seek interrupts.
These changes facilitate more robust parameter type checking and helps
to identify unexpected coding errors.
Most simulators can now also be compiled with a C++ compiler without
warnings.
Additionally, these changes have also been configured to facilitate easier
backporting of simulator and device simulation modules to run under the
simh v3.9+ SCP framework.
