bdr: mergme: Read the beginning and the lsn for feedback purposes
bdr: committs: mergme: Fix bogus pointer arithmetic
bdr: mergme: Make sure variables are initialized correctly in edge cases
wal_decoding: mergme: Increase slab cache size for changes

Rather noticeably increases bulk load performance
wal_decoding: mergme: Recognize multi_insert heap2 records properly

Previously we skipped decoding them when the INIT_PAGE flags was set...
bdr: replication origin: mergme: reduce log level
Lower log level for bdr_apply and make it configurable

affects:

'sending feedback'
'COMMIT origin'
'bdr_apply: BEGIN origin'

Per discussion on https://rt.2ndquadrant.com/rt/Ticket/Display.html?id=7202