passing twice test for negative-index .slice()
passing test for twice with sliceReverse
passing test for mixed slice() and sliceReverse()
mixed test also passes when the first slice is positively-indexed
passing test for a positive slice on a following file
another passing test for followed slices on negative indexes
passing test for sliceReverse() on an active follow
fix for reading the offset cache for negative end indexes
0.2.1