- update to 1.21.1:
* Reinstate '-I/--isolate' by popular demand; use at your own risk!
* Expect to lose data if you use this feature. It is strongly susceptible
to the documented "triangle problem" and absolutely does not protect
files in each directory from matching with one another. Don't get mad at
me if you use it and see a cloud of smoke come out of your disk array.
* Remove '-I/--isolate' which has never worked correctly
* Fix compiling when NO_HARDLINKS and NO_SYMLINKS are both defined
* Increased stack size limits to enable deeper recursion without crashing
* Fixes to make compilation under Cygwin (instead of MSYS2 MinGW) work
* Remove the temporary '-X help' warning about changes in functionality
* Some minor under-the-hood changes for future enhancements