Concatenate a relative path to an absolute path and remove any
"//", "/.." or "/." to produce a straightforward
absolute path as result.
combine_path_nt concatenates according to NT-filesystem conventions,
while combine_path_unix concatenates according to UNIX-style.
combine_path is equvivalent to combine_path_unix on UNIX-like
operating systems, and equvivalent to combine_path_nt on NT-like
operating systems.
column()