Major Description
1. Print the full path of the histfile on startup, \set, \push, \pop and \unset.
Allow -quiet to disable printing of these statements
2. Fix histfile for \unset.
Issue description : After \unset histfile, default to .cbq_history. Right now it continues using the latest histfile value, which is incorrect.
3. Fix \unset, \pop for histfile but never allowing the .cbq_history to be deleted as default.
Issue description : After \unset or \pop histfile, we default to .cbq_history. But \set; will display an empty parameter stack for histfile. This is incorrect. It should always contain the default entry after popping all elements or unsetting histfile.