Ignore .clog files - leftovers from vim
Alpha version of code to support -r %r

PostgreSQL allows you to use "%r" when calling restore program, which
signifies last important xlog file.
This can be used to remove all old, obsolete segments from archive.
Previously omnipitr-restore was doing this (removal) based on data from
pg_controldata, but relying on "%r" is safer, and faster.
Fix thinko in condition

Value is defined whever user uses "-r" as command line option. But there
is no sense in checking for validity of given xlog name unless the name
has actually been given.
Documentation update for o-restore's "-r %r"