debugrevspec: add option to skip optimize() and evaluate unoptimized tree This will help debugging optimizer bugs. Maybe '--no-optimized' can be changed to '--optimized' (default: True) when flags series landed.

revset: remove showwarning option from expandaliases() Now all callers pass showwarning=ui.warn, so we no longer need the option to suppress warnings.

debugrevspec: evaluate tree built by itself Prepares for new option to evaluate an unoptimized tree. Since a revset expression is no longer parsed twice, alias warnings should be displayed at the first parsing stages. That's why showwarning=ui.warn is added.