Add a check for 404 errors

[mbret]

Whenever gupm try and fail to access a dependency the script seems to never finish (or at least not within a reasonable amount of time).

It's stuck on the last red cross forever

Also could it be possible to squash the same type of message in the case they are repeating right after each other ? Maybe only display the first that says trying again and only shows the last one (after timeout). This way we reduce the console pollution

[azukaar]

Good one yes So there's two "bugs" (or missing features) here :

• GuPM doesn't try to identify 404 errors and simply retry downloading a package forever assuming that it exist
• g install mysql doesnt work yet because of #15 . When OS provider will be available and made default, it will

First one need a fix