Make ChromePHPHandler and FirePHPHandler sendHeaders flag static so that when multiple instances of the handler class exist they will all respect the one-time check that determines whether the handler should append its logs to the response header
Merge pull request #151 from ryanathasoffers/prevent_erroneosly_sent_FirePHP_and_ChromePHP_header_logs

Fix issue where ChromePHP and FirePHP handlers sent logs to ineligible browsers when >1 handler is instantiated