Append relative paths to an absolute path and remove any
"/." to produce a
straightforward absolute path as a result.
"../" is ignorded in the relative paths if it makes the
created path begin with something else than the absolute path
(or so far created path).
append_path_nt() fixes drive letter issues in relative
by removing the colon separator
":" if it exists (k:/fnord appends
append_path_nt() also makes sure that UNC path(s) in relative is appended
correctly by removing any
"//" from the beginning.
append_path() is equivalent to append_path_unix() on UNIX-like
operating systems, and equivalent to append_path_nt() on NT-like