[RFC] lib: don't allow xbps self-update to bypass integrity checks

[oreo639]

cc: @Duncaen

Right now, this is just a dumb implementation of the fix to get feedback, ~~this does not currently remove the xbps_autoupdate() mechanism.~~ Ofc if you prefer to go a different route (e.g. static linking) please let me know.

You can test this using libhelloworld and test1 from https://github.com/void-linux/xbps/issues/580 and then having xbps depends on libhelloworld>=<helloworld_version> where helloworld_version would be 1 for the first build and 2 for the second ofc.

Closes: https://github.com/void-linux/xbps/issues/592

[oreo639]

I made an alternative version where the self-update check is kept, but just made into a warning if that is preferable? https://github.com/oreo639/xbps/commit/8cb137a49c1a6eff83eb960677955c87cf18c368

[Duncaen]

Seems reasonable to make it a warning.