Add formal message categories to C++ Broker log messages

This is a proposal to add log categories to C++ Broker log messages.

Problem Statement

There are difficulties working with C++ Broker logging when appplying a log filter criterion. What precise FILTERTEXT can a user specify for:

--log-enable debug+:FILTERTEXT

Even after the fix from QPID-3891 it is not intuitive what to specify for a FILTERTEXT and any useful filter requires detailed knowledge of the source code.

Proposal

A log category is a high-level classification of the nature of the logged event that is not tied to a particular source module or code function name. This log category would become the target for FILTERTEXT log filters.

The following list is the proposed log category definition. Each log category name is followed by a list of source code directory names that would generally produce logs using that log category.

There is no strict rule that a module produce only log entries of a specific category.

The category would be inserted into each log message after the time of day but before the message text.

2012-03-06 16:55:38 [Management] SEND PackageInd package=org.apache.qpid.broker to=schema.package

A user could then filter log messages by using the category names:

--log-enable debug+:Management

This scheme would have a number of benefits:

1. On a per-message basis the filter comparisons would be using enumeration values and not strings.
2. The feature could be documented sensibly.
3. Log files would be easier to interpret manually or by event management systems.

The classifications could be phased in gradually. The current
QPID_LOG(LEVEL, MESSAGE) would produce [Unspecfied] events while the new
QPID_LOG_CAT(LEVEL, CATEGORY, MESSAGE) would produce events using an actual category.
Similar additions are made for the QPID_MSG entries.