Apache FOP Code add (bug 41044)

Code add
by
AD
(fixes bug 41044)

:

Partial application of the patch in Bugzilla 41044:
* addition of a generic PropertyCache to be used by all Property
types that can be safely canonicalized
* modified EnumProperty, StringProperty, NumberProperty, EnumNumber
and FixedLength to make use of the cache infrastructure
Thanks to Richard Wheeldon.