Place more msgs under cache_log_message control, downgrade some (#1273)

Place more msgs under cache_log_message control, downgrade some (#1273)

Also support cache_log_message-controlled messages in ::Config-unaware
libraries (e.g., libip) used by tools (e.g., cachemgr.cgi).

Restricting the very first (i.e. "depth 0") "Processing Configuration
File" message does not work during startup (before that file is parsed),
and does not work during reconfiguration (because the old configuration
is reset shortly before logging that line). Future reconfiguration
support improvements may fix the reset problem. Restrictions do work as
expected for included files (i.e. positive "depth" levels).

Restricting "BCP 177 violation" WARNINGs does not work because the
warnings are printed _before_ Squid configuration is parsed. Future
initialization improvements may fix this.

Also downgraded the importance of a few (re)configuration
progress-reporting messages from level 1 to level 2.