Misc (re #1751): Fix build error (Ubuntu 14.04) when building Pjsip with OpenCore-AMR.Thanks to Alexander Traud for the patch.


git-svn-id: http://svn.pjsip.org/repos/pjproject@4833 74dad513-b988-da41-8d7b-12977e46ad98
Re #1762: Add capability enumerations and native preview capability



git-svn-id: http://svn.pjsip.org/repos/pjproject@4834 74dad513-b988-da41-8d7b-12977e46ad98
Re #1757: Avoid calling OpenGL ES functions when in the background (which may cause app to be killed by iOS)



git-svn-id: http://svn.pjsip.org/repos/pjproject@4835 74dad513-b988-da41-8d7b-12977e46ad98