[test] fix GLOB* temp file creation

regression from commit caba76f589a9aa.
mixed up handle and filename, as run_command actually requires
a name and not a handle for STDERR.
[docs] Update stability and memory_internals

stability was written in 2007. Just the deprecation cycle
needed to be updated.

memory_internals talks as if mark&sweep is the only GC.
Improve that.