Revamp and reduce log messages (was: Not clear that fail-over is working)

Problem

• Logged errors are confusing for users, if the module recovered from them.
• (Too) Many debug messages are logged and shown by dblog.module (by default in D7; not filterable in D6).
• Primary logged message is not clear.

Goal

• Log only one message per request (or high-level action performed).
• Make the single log entry show the primary message first.
• Retain additional messages within the single log message (i.e., append them).

Details

• Mollom produces a lot of log messages. Mainly for debugging purposes in case of errors or when a post is treated inappropriately.
• A single Drupal request may trigger multiple Mollom requests being logged, as well as "functional/primary" log messages generated by the business logic of the module (e.g., "Unsure: %teaser").
• Users complain about the amount of log messages. The amount is not an issue for syslog, but can be an issue for dblog on large-scale sites.
• The module recovers from certain errors, but it also logs any errors that occur, regardless of whether the final operation is successful or not.
• Most logged messages are debug messages, primarily important for functional module tests.
• For Mollom support requests, it is helpful to see the entire stack of operations that were attempted.
• Most messages are logged within form processing, but some others are logged outside of the Form API scope.

  E.g., when an entity gets ultimately inserted or deleted, my.mollom.com may be informed about that, which triggers a separate log message.

• The original cause for this issue is obsolete, since the client-side server fail-over logic has been removed.

OP by @Dries

When looking at the watchdog, it is not clear that the fail-over is working. Quite the contrary, people might believe that Mollom might be down or broken because they sometimes see error messages. I think we should make it more clear that the fail-over is working.