Grow maximum count to be at least the count of entries that will fit in a chunk.
Introduce the concept of in use entries.

Entries that are in use are immune from eviction. This concept is needed
to protect the bits that are currently being referenced by a UIImage/CGImageRef
from being overwritten.

Note also that inUse is a refcounted concept since multiple FICImageTableEntry's
can be allocated against the same entityUUID/bits in the backing file.

A side effect of this change is that the imageFormat's maximumCount is no
longer a hard limit since it is possible that all maximumCount entries could
be in use.
Declare an entry in use for the remainder of its lifetime after it is used
with CGDataProviderCreateWithData.
Style change to make release of retained FICImageTableEntry more clear (i.e.
use ARC to perform release rather than explicitly calling CFRelease since
that's what you do with NSObject's).
Merge branch 'evictionbugs'
Debug dump methods.