A small refactoring to reduce diagnostic output.

Added new configuration option in the section "resources":
dap_global_db_track_history=true|false (default is false)

dap_common.h:
Added new macro debug_if(cond, log_level, format, ...) is supposed to be used instead of
giant construction like:
if ( debug_flag )
 log_it(L_DEBUG, "bla-bla-bla");