Idiot proofing the input queue

[KPJoshi]

The changes are in individual commits and can be selectively undone if necessary. This might be necessary if the behavior that I have modified was the intended behavior.

I have made the following changes:

• fwd will do nothing if the input queue is empty, instead of entering an error state
• new and dup will do nothing if the input queue is full, instead of overfilling the queue
• dup and drop will do nothing if the input queue is empty, instead of entering an error state