Update setup.ini when necessary

If you tried to use this command

    apt-cyg install --mirror <URL> <package>

with a new mirror, it would fail because "apt-cyg install" no longer downloads
setup.ini every time. Fix so that setup.ini will be downloaded if it does not
already exist.
Revise remove command

1. print a list of all files and dependencies of those files used by apt-cyg
2. if any are found in the files list of the package to be removed, then fail

Unrelated, added an echo each time a postinstall script is run, the name of the
script