[PATCH] add configuration option to enable/disable glamor in xwayland

[Mildred Ki'Lya]

Following bug #86815 https://bugs.freedesktop.org/show_bug.cgi?id=86815 
where xwayland is very slow on eee-pc with not enough hardware support 
to get by, I created a patch to add an option in weston.ini to disable 
glamor.

The configuration is:

     [xwayland]
     enable_glamor=true|fase

The patch applies cleanly to both latest HEAD and tag 1.6.0.

Could you consider including it?

Thank you,

Mildred