If a marker file indicates that an installer has been downloaded and verified
and is ready to install, but that installer file does not exist, log it and
revert to checking for update.
Also add logging to every code path that can remove the installer explicitly,
in case the missing installer is actually being killed off by some weird
sequence of state-machine transitions.

Also, delete it when done.

MAINT-3412 Fix Intel Iris recognizer to include optional Pro as is reported with integrated-only graphics on new MBP

MAINT-3376 FIXED Successive llSetTextureAnim calls fail in 3.6.10 (283075) unless a different command (llSleep(0.01), llSay(0,"hello")) is placed between them.:
 - fix for MAINT-2861 was reverted to resolve this issue;

MAINT-3356 GPU Table update to support Retina MBP 'Intel Iris OpenGL Engine' driver id on Mavericks.