ensure standard shell is used under windows to pass correct glob command

Dear Szymon,

This commit ensures that under MS Windows always the standard shell (that is 'cmd' and not 'powershell', 'Korn Shell', ...) with standard parameters is used to invoke all bang commands. 

Otherwise, for example the glob command fails, if customized by the user.
I think we should stick with the existing convention (snake case). Perhaps the name `shell_save` would fit better here?