Reviewed by Simon Hausmann.

        Rename the plugin logging channel to plural form 'Plugins'

        This matches both the other logging channel names, as well as the
        WebKit logging channel used by Safari/Mac for plugins.

        * platform/Logging.cpp:
        * platform/Logging.h:
        * platform/gtk/LoggingGtk.cpp:
        * platform/mac/LoggingMac.mm:
        * platform/qt/LoggingQt.cpp:
        * platform/win/LoggingWin.cpp:
        * plugins/PluginDebug.h:
        * plugins/gtk/PluginPackageGtk.cpp:
        * plugins/mac/PluginPackageMac.cpp:
        * plugins/mac/PluginViewMac.cpp:
        * plugins/qt/PluginPackageQt.cpp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@44988 268f45cc-cd09-0410-ab3c-d52691b4dbfc