[Mesa-dev] V2 More shader cache improvements

[Timothy Arceri]

This is a resend of version 2. The follow is some load/start-up times
gathered by Grazvydas Ignotas. I was seeing similar results as noted
in the commit messages.

               before    after
               cold hot  cold hot
DeusExMDbench: 285  34   261  27
Talos:         20   20   18   17
L4D2_lvl:      19   19   19   18
AlienIsl:      27   18   24   17
AlienIsl_lvl:  47   26   43   23
SOMA:          14   14   14   14
SOMA_lvl:      13   13   13   13
TombR_lvl:      7    5   7    5

Note: _lvl indicates some saved game level load times from the main
menu.