Improve session detection logic

Process.terminal() returns the path to the terminal attached to the
process, if one exists. This will include most processes launched
interactively, not just processes that represent sessions. This
implements a new heuristic, in which a process is a session if it has a
terminal attached and either somehow has no parent or its parent has a
different terminal attached. This heuristic is probably not foolproof,
but should be sufficient for the majority of cases.

tracer/resources/processes.py

@@ -245,8 +245,12 @@ def is_interpreted(self):
 
 	@property
 	def is_session(self):
-                if self.terminal() is not None:
-                        return True
+		terminal = self.terminal()
+		if terminal is None:
+			return None
+		parent = self.parent()
+		if parent is None or terminal != parent.terminal():
+			return True
 
 	@property
 	def real_name(self):