Minor cleanup item noticed playing over in
ReplicationSource has an inner class named LogComparator which is a pretty generic name for the comparator only it just compares on WAL start time and nothing else.
Also, messing in
HBASE-18070 I ran into compares that included user-space WALs and hbase:meta WALs. The LogComparator as is barfed on meta WALs.
This ticket moves the comparator to AbstractFSWALProvider, where folks will go looking if they need WAL comparators, and it also renames it to more clearly explain what it does (and makes it so it can compare start times even if it a meta WAL).