tools/ftpserver.c: Bug fixes, refactoring and improvement

[robert-hh1]

tools/ftpserver.c: Normalize path names

Path names supplied with ftp commands will be normalized, causing:

• excess slash characters to be removed
• . path elements to be removed
• .. path elements backing up the path one level

tools/ftpserver.c: Refactoring of ftpserver.c

Consisting of mostly editorial work and additional checks

Removed

• commented out code

• if 0 deselected code

• code for WIN32

Optimize LIST and NLIST

Both commands use the same function now, which is told by
a parameter which format to use. This function do_list() now
also receives a buffer for temporary strings, reducing it's stack
usage.

Always build pathname from the parameter

Since many commands use the parameter as filename, build it
always. It does not hurt, if the parameter is not a filename, since
building the path has no side effects.

Checks: Check, that the resulting path created by build_full_path() does not exceed the buffer size.

Test, that the target given with CWD exists and is a dir

Bug fixes:

• do not call chdir(). Just change the session->current_dir variable
• use the full path name as target for rename

[robert-hh1]

I'll update that for a more concise version.