exctra cpu load with __gl_meshCheckMesh

according to perf, __gl_meshCheckMesh add extra 4% of CPU overhead on empathy-call. At same time complete libvpx (vp8 video encoder) takes 9%.
Since it is debugging function, it can be disabled by adding "#defining NDEBUG" to the source.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: libcogl12 1.14.0-2
Uname: Linux 3.12.0-rc3-wl x86_64
ApportVersion: 2.12.5-0ubuntu2.1
Architecture: amd64
Date: Sun Oct 27 20:16:56 2013
InstallationDate: Installed on 2013-10-09 (18 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Beta amd64 (20131008)
MarkForUpload: True
SourcePackage: cogl
UpgradeStatus: No upgrade log present (probably fresh install)