Windows Git users with symlinks have a constantly dirty repo from
this "a_symlink". This change generates a symlink in the build directory
when the test is run.
D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
is_samepath better reflects the nature of this function--that files
and directories can be compared.
Also, instead of raising exceptions, simply return False when one
or both .is_samepath(path1, path1) don't exist. This is more
intuitive behavior and avoids having an extra if fs.exist() to go
with every fs.is_samepath()