Fix fakeroot messing up a test by moving it to the unsafe area.

Fakeroot's file magic somehow interferes with the backgrounded
promises which in turn leads to stale processes lingering after the
test has finished.
readfile and textxform functions do not rely on 4k limit anymore
Added text_xform tests for large sizes
CF_INFINITY is not a limit for buffer size, it's just an indication that policy has the parameter 'inf'.
Comment for clarity.
A couple of TODOs.