[PATCH] Move a misplaced #define in libsvn_delta/compose_delta.c

Patch by Refael Ackermann (mose_at_netvision.net.il).  Moves a #define from
compose_delta.c to delta.h, and guards it with a #ifndef.  Greg Hudson replied
saying that the #ifndef guard was understandable, but questioned the move to
delta.h.

The original patch is archived here:
http://www.contactor.se/~dast/svn/archive-2004-10/0109.shtml

and a revised version of a confusing comment in the patch is here:
http://www.contactor.se/~dast/svn/archive-2004-10/0108.shtml

http://www.contactor.se/~dast/svn/archive-2004-10/0109.shtml

Original issue reported by mthelen