Add missing include for options.h in chunk.h

Not including this file would cause errors if the chunk allocator was
enabled, since chunk_reference_t would have the wrong type and cause
all sorts of interesting chaos. This is one of many reasons the C
preprocessor is evil.

git-svn-id: https://pennmush.googlecode.com/svn/trunk@1778 ba372814-4f39-11de-9ad6-1127a62b9fcd