Fix rare potential NPE in HHOM page size calculation

patch by Aleksey Yeschenko; reviewed by Jonathan Ellis for
CASSANDRA-7354
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
Merge branch 'cassandra-2.1' into trunk