Fortran filesystem

Numerous internal corrections and efficiency improvements. Improve test coverage.

add is_prefix(), is_appexec_alias(), is_fifo(), space_capacity()

rename() clobber destination if it exists

correct mkdir() permissions check

Windows: detect and use correctly App Execution Aliases

which: find_all = true now returns all matches instead of default first match only

which(): on Windows use SearchPath() to find executables

Windows: is_reserved() bugfix "." is not reserved

Windows: is_symlink() distinguish between reparse points and symlinks

is_exe(): file or directory can be executable