kes Added the following to provide solutions to the plugin/Accurate

kes  Added the following to provide solutions to the plugin/Accurate
     problem -- bug #1236 Cannot restore incremental backups with
     the Exchange plugin.
     - New Bacula read-only variable bVarAccurate -- returns accurate flag
     - New Bacula write-only variable bVarFileSeen -- marks a file as seen
     - New plugin entry point -- checkFile that is called at the end
       of an Accurate job and allows the plugin to mark a file as seen.