Fix #11527 initialize posix aliases after a %reset

[jwidner]

Changes the behavior of %reset by initializing the posix aliases clear, less, more, and man during a reset. It's not clear to me what the intended behavior should be, but it fixes #11527.

[Carreau]

That seem reasonable to me. Thanks.

[red8012]

It seems that the change causes the following message being printed whenever a reset is done.

ERROR:root:Invalid alias: The name clear can't be aliased because it is another magic command.
ERROR:root:Invalid alias: The name more can't be aliased because it is another magic command.
ERROR:root:Invalid alias: The name less can't be aliased because it is another magic command.
ERROR:root:Invalid alias: The name man can't be aliased because it is another magic command.

See https://stackoverflow.com/questions/54971047/spyder-reports-invalid-alias-when-running-any-script. The issue happens not only on Spyder but also on Jupyter notebook.

[Carreau]

Can you please open a new issue for this ? Thanks.