icasefs: make case-folding collision detection as rename aware (issue3370) if the file in target context causes case-folding collision against one in working context, current implementation aborts merging with it, even thouhg collding one (in target) is the file renamed from collided one (in working). this patch uses file copy information to know whether colliding file is renamed from collided one or not: if so, collision between them is ignored. this patch also avoids collision detection between current context and target context, if working context is clean (with --check/-c) or will be clean (with --clean/-C).

bdiff.bdiff: release the GIL before doing expensive diff operations This means that threaded webservers will have more of a chance of doing something useful while the C extension is busy computing a delta. Not doing this was causing problems for Google Code with a 25 meg text file that takes O(7 minutes) to deltify.