Error codes should now be in certain ranges according
to their use, e.g. messages intended to be sent to the
client are expected in the range below 10,000, while
messages intended for the error-log are expected in the
range starting at 10,000, and so on.

A number of messages were recently added in unsuitable
ranges. This patch therefore endeavors to achieve three
things:

- Provide an assert() in the function reporting to
  the client that will error out if the provided
  error-code is in the server-range. (An assertion
  already existed, but let pass the aforementioned
  false negatives. This patch fixes that.) This is
  considered a workable solution as code that reports
  to the client is as a rule expected to cover those
  code paths in the test suite.

- Move the messages in question to the correct ranges.

- Provide a simple utility that scans source files
  for calls to LogErr() / LogEvent() (the server's
  calls to the error-logger), extracts the symbols
  for any calls found, and looks up those symbols
  to make sure they exist and are in the correct
  range. The reasoning here is that test coverage
  for paths involving the error logger is lower than
  for messages to the client (as the situations that
  result in these message are often hard to trigger
  without DBUG_EXECUTE_IF / @@session.debug, such as
  out of memory situations). While the tool was
  originally written to ensure that all
  mis-categorized log-messages were covered in this
  patch, it is provided here for optional use by
  individual engineers, or for adding to the
  repository's hook.

Approved by: Jens Even <jens.even.blomsoy@oracle.com>