SystemTools: Fix FileIsDirectory with long paths
SystemTools: Fix FileIsDirectory with long paths

Allocate a buffer large enough to hold the input path when removing a
trailing slash.  Use a local stack buffer when it is large enough and
fall back to heap allocation otherwise.

Change-Id: Ibc4b4c96c7b0fafae9f4b5cd7ea894bdd605a098

chuckatkins/KWSys,chuckatkins/KWSys,chuckatkins/KWSys,chuckatkins/KWSys