Disable compositing mode in WebKitGTK < 2.13.4
Disable compositing mode in WebKitGTK < 2.13.4

Some websites may crash system with it:
https://bugs.webkit.org/show_bug.cgi?id=126122

Note that WEBKIT_FORCE_COMPOSITING_MODE is honoured since WebKitGTK
2.10.5: https://trac.webkit.org/wiki/EnvironmentVariables

Issue: tiliado/nuvolaplayer#245

Signed-off-by: Jiří Janoušek <2a48236b6dcae98c8c0e90f4673742773ee17d91@gmail.com>

tiliado/nuvolaruntime,tiliado/nuvolaruntime,tiliado/nuvolaruntime,tiliado/nuvolaruntime