* src/ftp.c(getftp): Don't free `target`. If it is not pointing to
targetbuf, then it still pointing to its original location of u->dir.
This location will be free'd later. Doing so now causes a double free
and hence crashes Wget
* tests/Test-ftp-dir.px: New test to show double free error
* tests/Makefile.am: Add new test
