Switch away from OS.File for (potentially) large writes

- osfiler wasn't a great idea.
- Switch chunk back to AsyncStreamCopiers
- Switch OS.File.move to the (re-)new(-ed) support/movefile (which has
  an own dedicated OS.File worker)
- Add some tests

git-svn-id: https://code.downthemall.net/repos/trunk@3736 43940e1f-b481-bb45-89eb-5c6a4bf3d40a
Fix MemoryReporter.memoryPressure

git-svn-id: https://code.downthemall.net/repos/trunk@3737 43940e1f-b481-bb45-89eb-5c6a4bf3d40a
Avoid __proto__ in FilterManager

git-svn-id: https://code.downthemall.net/repos/trunk@3738 43940e1f-b481-bb45-89eb-5c6a4bf3d40a
Fixup buffer_size in chunk

git-svn-id: https://code.downthemall.net/repos/trunk@3739 43940e1f-b481-bb45-89eb-5c6a4bf3d40a
Fixup add-on shutdown (in case of fast shutdown)

git-svn-id: https://code.downthemall.net/repos/trunk@3740 43940e1f-b481-bb45-89eb-5c6a4bf3d40a