enet: Search for shared library

[degasus]

No description provided.

[comex]

I don't think this is a good idea. There are a few modifications to enet I want to make soon:

• IPv6 support - some enet forks have implemented this (like, there is an almost 2 year old PR), but upstream doesn't have it. IMO, in 2015 no new application should omit IPv6, so this is important.
• Opportunistic resending - the current merged enet-using code doesn't have this at all. My original enet branch supported it using a wrapper around stock enet, it would be more elegant and have a bit less overhead to do it in enet itself (it wouldn't require changing the protocol). This might be counteracted by the benefit of being able to use stock enet, but considering the first point...

[degasus]

rebased.

@comex I think we should try to not fork our externals if possible. Are those features possible to include within enet directly? So projects will win.
However, do you want me to drop this part of the PR or will you just revert it when you're going to break enet compatibility?

[comex]

Well, I can try. The problem is that judging by the history of this pull request:

lsalzman/enet#21

I'm not too enthusiastic about upstream accepting patches.

But maybe if I implement IPv6 without breaking ABI compatibility, @lsalzman will be more interested.

[degasus]

@comex So do you think this should be merged as it is or shall I remove the global enet usage? I mean you're always free to revert this change on forking enet.