bugs quality lines of code gcc mining challenge developers msr challenge mailing lists size evolution argouml coordination gnome social network analysis apache prediction cvs contributions Firefox motivation bug tracking eclipse source code project success social networks kde mining software repositories bug fixing linux kernel core bug reports open source software education metadata email contributors linux software evolution java freebsd scm floss metrics Debian oss2009 sourceforge netbeans case study postgresql flossmole bugzilla roles mailing list survey Mozilla version control open source loc email archives python