Make sure hot_standby_delay doesn't return negative values

Before this patch, the hot_standby_delay action could return negative values.
To minimize the risk, we first query the slave, then the master. And to make
sure, we never get negative values, we set them to zero if we have a negative
value.

Report and ideas from Filip Rembiałkowski.
Bump year to 2013 and some minor HTML adjustments.
Fix userclause handling in check_txn_idle

For databases > Postgrs 9.1, irrelevant records are discarded
with two ORed conditions. This makes the optional userclause
associate with the right hand side of the condition. The expression
needs to be grouped to get the desired effect regardless of the
evaluation of the previous condition.
Credit recent change
check_txn_idle: fix query_time --excludeuser query

Parenthesis are required:

"a OR b AND usename <> 'foo'" -> "(a OR b) AND usename <> 'foo'"

Fixes at least "query_time --includeuser/--excludeuser".
Credit recent change
Get rid of "uninitialized value" warnings.
Credit recent change.
  Fix the check_bloat SQL to take inherited tables into account, and assume 2k for non-analyzed columns.
Better debug output: check for dbdir and datadir separately.
Force tests to use port 5432 in case PGPORT is conflicting.
Adjust docs from earlier remote merge.
Force slave to be defined, per github issue 19: https://github.com/bucardo/check_postgres/issues/19
Don't assume that everyone has a home. Per github issue #23
Don't barf when schema does not exist.
Minor tweaks to get ready for 2.20.0
Manifest tweaks.
Signature for 2.20.0
New signatures
Make sure connection checks return CRITICAL rather than UNKNOWN.
Patch by Dominic Hargreaves with minor tweaks by Greg Sabino Mullane.
Thanks to Christoph Berg for the forward (this came in via the Debian bugs system)