Test more variants to specify the root directory.

Test realpath and unveil if the root directory is written as "//".

Fix realpath(3) errno code for an empty input path string.
It should return ENOENT in this case, but was returning EINVAL.
ok bluhm@ deraadt@

Our kernel __realpath(2) implementation does not allow non-existing
files anymore. This is conforming to POSIX. Adjust the regression
test to the new behavior.
OK beck@

Regress realpath(3) fails since the non directory hack has been
removed from libc. Make the regress implementation more POSIX
compliant like it has been done for the kernel.
OK beck@ deraadt@

Fix white spaces.

Add some more relative path tests

Document our currently incosnsistent behaviour and our current
sins which have been judged by Dr Posix as sinful...

let's check /bin/c++

Add another case for robert@ :)

a bit more evil

/usr/include/machine is a good one.

Start a realpath(2) regress test, currently not enabled.

This will extend as I add more cases to it. It will come
into use once an in-kernel version of realpath(2) becomes
a real thing