Add cgame/qgame version check

[ETLegacyTeam]

Author: @rmarquis (Spyhawk)
Date: 2019-03-20
Redmine Issue: 1225, https://dev.etlegacy.com/issues/1225

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Version string of UI/cgame/qgame are displayed in console by default.
Try checking for cgame/qgame version match, and print a warning if that isn't the case (console, or maybe even in the center screen?).

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Related commit(s):
e8fec93 - mod: added mod version mismatch check, fixes 1225..
50c4a35 - game: ensure dropped client isn't processed, refs ..
f335fe7 - misc: use fixed git version length, refs 1225
7134696 - mod: revert cgame/game version check, refs 1225"..
ea44ba9 - client: store engine and mod versions in userinfo,..
17ee01f - general: add engine version verification facility,..
3c14fb6 - game: added cg_etVersion info display in /players
6f1da27 - game: fixed version info display in /players for b..
6319f49 - client: fix regression where on server disconnect ..
e9489ee - general: fixed engine client version overwritten i..
6a1eab0 - client: removed now unnecessary etVersion in clien..

[ETLegacyTeam]

From: @rmarquis (Spyhawk)
Date: 2019-03-28T09:08:42Z

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See the already implemented (but disabled) G_CheckVersion() function.
Rather than a print, drop the client with a clean message (better than the actual "unknown event 67").

[ETLegacyTeam]

From: @rmarquis (Spyhawk)
Date: 2019-04-26T22:05:07Z

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Applied in changeset commit:e8fec93efc31996db725a0534e2ffe590e6aee2b.

[ETLegacyTeam]

From: @rmarquis (Spyhawk)
Date: 2019-04-30T16:00:47Z

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Note: Newer git versions (2.11) seem to have a different output than older version (f.e. 2.5), with 8 hex digits rather than 7 (dynamic length). This is problematic when compiling the game on older platforms like CentOS 7.

Edit: thie is also problematic when used as a dev, with older downloaded bin versions preventing dev version to be launched locally. Inspect again once the contanerized FS is fully implemented.

Also, the engine version check might actually be important to keep (2.55?).