dbglog: Added separate macro for enabling debug log. [FIXED]

This fixes commit 'e8557a6a489106b7ef6 dblog: Added seperate macr...' which actually broke the debug log for all channels that were not explicitly registered via the environment variable.

I misunderstood how dbglog works, so I ended up breaking it by trying to 'fix' what wasn't there. The old and new commit together have the effect of only adding the macro DEBUG_ENABLE_MESSAGES to enable the dbglog.