Intermediate commit: un-revert last change

Change-Id: I3d18f8d6844377edc0864d81284c7fb9dbb9dbf9
CF_TRACE also the CFRetain to avoid confusion

Change-Id: Iae712de4efbbe254ba381a036e2c84d5e27d5e40
Mention early exits in the verbose debugging log

Change-Id: I68e5aa92cb6ccff8b8d077c311d2ebc3f4676ae7
Set mbPrinter anc mbVirDev for iOS, too

But, has no visible effect, doesn't fix rendering problems.

Change-Id: Ic79b38b665e357a2dafe679c35979250c3bff538
More iOS-only debugging hackery: write CGImages out as PNGs for inspection

Change-Id: I966189a74414ea83b2ec7f5035cd7c9d4d674179