POSIX: Add $SNAP to search path if available.

[fuzzie]

This allows ScummVM to find data files while running in a snap (e.g.
from the new Ubuntu store).

[fuzzie]

This should respect the prefix, and the snap path should be higher priority than the data path added by the superclass. I'll fix these shortly.

I think it makes sense to keep the data path in the search path, to avoid breaking things if someone has $SNAP set to something random. That's easy enough to change too, though.

[sev-]

Why not reverse the condition?

edited

ignore me, you have the fallback.

[wjp]

It should still call OSystem_SDL::addSysArchivesToSearchSet even when SNAP is not set.

[sev-]

Nice, merging.

[rootfather]

@fuzzie, @spads-spads: Do you consider the snapcraft support to be stable enough to be mentioned in the Linux port section in our NEWS file?

[spads-spads]

@rootfather It's stable enough that I've been able to build arbitrary revisions from git and play Beneath A Steel Sky on them. There's work to be done to tighten the access required, so we can snap up self-contained games with scummvm inside so they don't need external filesystem access.
But from a simple packaging formats standpoint I think this is stable enough to announce!

[rootfather]

@spads-spads Thanks for your reply. If you don't have any objections, I'll mark the snapcraft support as "preliminary" or "basic" in the appropriate NEWS item until full functionality is achieved.

[spads-spads]

Sounds good!