Migrate pre-2.0 key/value/column aliases to system.schema_columns

patch by Aleksey Yeschenko; reviewed by Sylvain Lebresne for
CASSANRA-6009
Fix typo
Paging filter empty rows too aggressively

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6040
Merge branch 'cassandra-1.2' into cassandra-2.0