prevent package conflicts when linking and uninstalling

[soraxas]

This PR is aimed to prevent packages conflicts; namely, when two different packages has identical names for binaries/man/completions.

This means avoid the -f flag in ln to NOT overwrite when file exists (a user should resolve packages conflict on their own), and when uninstalling a package it will checks that: if the link to be removed is indeed from the package that we are uninstalling (by resolving the link).

[juanibiapina]

Thank you! You're right, -f should not be used. If you're still interested, please add tests and I'll merge it.