MFC r312521,r313397:

r312521:

Add testcases for -i with hardlinks and symlinks

The symlink testcase is expected to fail, post-r312519 (the revert of
r312404); mark it so.

r313397:

Don't expect :inplace_symlink_src to fail anymore (post-r313277)

The S_ISREG check was restored, such that the code will again fail with
in-place replacements on symlinks