Fixed the testsuite up somewhat.
(1) Moved helper code into separate file.
(2) Replaced helper code blocks in variables with proper procedures.
(3) Simplified setup1, cleanup1
    No need to search for and create lots of temp dirs in setup,
    just remove the directory in cleanup. Now use single temp dir,
    fixed name.
(4) Fixed setup of tests in general
(4a) Added emacs mode marker to get proper Tcl mode.
(4b) Added missing Tcl 8.5 requirement
(4c) Use canonical 'use' command for access to local package (memchan).
(5) Constrained the one test requiring Tcl 8.6 (zlib)

It is not yet clear to me why the 'stream' helper (to create a large
file) is so complex.