Added omnipitr-checksum

This program makes it simpler to add checksums from within
omnipitr-backup-*, and it can also be easily used as standalone.
Create $self->{'meta'} for storing metainformation

Now, just starting time is in there (in ->{'started_at'}), but there will
be min/max xlog filename too.

This information will later on be stored in "meta" files, which will be
used for backup retention policy.
meta data captured

So far it's not delviered to any destination/files, but it's there already
so that it can be used later on.

Gathering seems to work for both master and slave, with slave both -cm and
without -cm, and with or without xlog backup.
perltidy run
Add missing module

without it, in some rare cases, code could error out
Added support for metafile generation

New file gets saved to all destinations, at the very end of backup
generation (after remote deliveries of data/xlog/checksums).
Merge branch 'backup-retention'

Meta files are now generated for backups