same presentation when logging on screen or file, 
making sure that it all stays in one line (to allow grepping easily),
adding unique request key as part of log line,
outputting current _REQUEST at the end of front controller init()

git-svn-id: http://dev.piwik.org/svn/trunk@4471 59fd770c-687e-43c8-a1e3-f5a4ff64c105