deal with an edge case when people typed unknow short options.
deal with an edge case when people typed unknow short options.

For example:

    > perlbrew -l
    Unknown command: `_l`. Typo?

That "-l" was kept forever and the same error message keeps poping out
for all further perlbrew invocations.

dagolden/App-perlbrew,ptolemarch/App-perlbrew,Asuza/App-perlbrew,Asuza/App-perlbrew,dagolden/App-perlbrew,calid/App-perlbrew,ptolemarch/App-perlbrew,Asuza/App-perlbrew,rafl/App-perlbrew,rafl/App-perlbrew,josl/App-perlbrew,josl/App-perlbrew,rafl/App-perlbrew,ptolemarch/App-perlbrew,calid/App-perlbrew,josl/App-perlbrew