StackInterpreter:
Simplify and make robust display bitmap access for display update.  The old code
required platforms that needed to redraw at arbitrary times to have to access
the display bits through interpreterProxy->displayObject, decoding it each time.
There exists a small window during compaction, etc, during whiuch such access
will fail and cause a VM crash.  The new code provides four variables to
reference the display, displayBits, displayWidth, displayHeight and
displayDepth, which are assigned appropriately in the primitiveBeDisplay
primitive.  After a GC the interpreter checks if the displayBits have changed
location and if so calls ioNoteDisplayChanged:width:height:depth:
(ioNoteDisplayChangedwidthheightdepth) to inform the platform of the change
(currently all platforms implement this as a null function).

On Spur the primitiveBeDIsplay primitive also pins the display bits.

This scheme allows displayBitsOf:Left:Top:Right:Bottom: to be simplified to
updateDisplayLeft:Top:Right:Bottom:.

On Mac OS X and X11, replace access to the display Dits via displayObject with
direct access to displayBits, displayWidth, displayHeight and displayDepth vars.

Spur:
Fix cloneInOldSpaceForPinning: to handle failed allocations correctly.
Have pinObject: only clone an old space object that is 1Mb or less, simply
pinning larger objects (whioch would include the display bitmap) where it sits.

Lift the limits on Spur image segments.  There is now no limit on the number of
objects in a segment, but the classes in the segment must occupy no more than
2 ^ 21 bytes (maxIdentityHash / 2 * 8 - which allows for about 1.4 million
11 slot classes), and the segment can have no more than 2 ^ 21 out pointers
(again maxIdentityHash / 2.  Tested for simple examples. Manages to export a
project but not load it yet.

Fail if the segment store args that are mutated are either immutable or pinned.

Fix bad bug in shorten:toIndexableSize: (which could affect Scorch/Sista).
The old code for addressAfter: would be fooled by an object with overflow
slows but fewer slots than numSlotsMask.  So fix addressAfter: so it will
still add the overflow header if there is one.

Rewrite objectBytesForSlots: to follow the fixed addressAfter:.  The code
should be cleaner.

Fix checkInterpreterIntegrity in the case of the primitiveDoPrimtiive code
setting newMethod to an integer.

Fix some translation-timer warnings by tweaking storeLiteralVariable:withValue:,
storePointerImmutabilityCheck:ofObject:withValue: & primitiveGetenv.