JBIDE-14663 : don't schedule file download twice

also skips source lookup for maven projects

Signed-off-by: Fred Bricon <fbricon@gmail.com>
JBIDE-14663 : catch CoreException instead of Exception

Signed-off-by: Fred Bricon <fbricon@gmail.com>
Reduce log pollution when sources not available

Signed-off-by: Fred Bricon <fbricon@gmail.com>
JBIDE-14682 : run file identifiaction in background job

Signed-off-by: Fred Bricon <fbricon@gmail.com>
JBIDE-14684 : remember last source lookup

Signed-off-by: Fred Bricon <fbricon@gmail.com>