clarified messages streaming (again, amending 5ea3ed3c52b3): avoid too many small messages stacking up, e.g. when loading HOL-Analysis.Analysis.thy into Isabelle/jEdit;

tuned signature;

support for bulk operations: consume mailbox content in batches;

clarified signature -- more explicit types;

more general dispatcher operations;

discontinued unused / untested distinction of separate PIDE modules;

clarified modules;

--HG--
rename : src/Pure/Concurrent/simple_thread.ML => src/Pure/Concurrent/standard_thread.ML
rename : src/Pure/Concurrent/simple_thread.scala => src/Pure/Concurrent/standard_thread.scala

more tight Mailbox: single list is sufficient for single receiver, reverse outside critical section;

more systematic Isabelle output, like in classic Isabelle/ML (without markup);

replaced manager Actor by Consumer_Thread, which is lazy to defer its start to actual Handler init time;

misc tuning;

support for requests with explicit acknowledgment (and exception propagation);

more robust thread: continue after failure;

allow more control of main loop;
more robust is_active test, although thread could terminate at any time;

more robust shutdown;
less ooddities;

consumer thread with unbounded queueing of requests (similar to Message_Channel in ML);