* Since we now use import-each, do not regenerate stdlib on each pass
 * Support all combinations of lower, upper and step values in both
   getting and setting slices
 - Avoid generating extra load() line in jsprinter, since this will
   lead to double-loading the stdlib. This makes the test suite take a
   full second less!
 * Updated list slice tests
 - Removed assign_slice_step from KtF
 + Implemented $PY.indices() which compute the start and stop indices
   for a slice on a given length. It is surprisingly hard to get
   right, so I used the CPython algorithm as an inspiration. Funnily
   enough, the sliceobject.c from CPython has the comment "This is
   surprisingly hard to get right". No kidding.
 * Make slice object use $PY.indices()
 + Added support for __setslice__ in list. It now uses $PY.indices()
   to get the correct indices.
 * Makefile clean target now keeps py-builtins but removes more cruft
 * Fixed filename in clean target
 * Do not eat first code line, now that jsprinter does not output spurious load()