1) Add a new flag in the sarea (coopting the unused texAge value) to

1) Add a new flag in the sarea (coopting the unused texAge value) to
identify context switches between members of a share group -
ie. multiple contexts in a single application, possibly on different
threads.  In this case the contexts share a bufmgr instance and there
is no need to evict textures - so don't.

2) Use a new flag 'need_flush' to ensure hardware rendering is flushed
prior to starting a software fallback.