Description:
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In response to the PASV command, FTP servers sometimes return their IP address 
(10.X for example) and PHP honors this IP address, stores it in ftp->pasvaddr 
and uses that for future connections.

This is problematic because PHP won't be able to communicate with a server 
behind a NAT device using passive FTP.

The attached patch adds the USEPASVADDRESS option (a boolean) which can be set 
and read via the ftp_set_option() and ftp_get_option() functions. USEPASVADDRESS 
is set to TRUE by default to preserve existing functionality. When 
USEPASVADDRESS is set to FALSE, the ftp extension will ignore the IP address 
returned by the PASV command and instead use the IP address passed to 
ftp_connect() (or ftp_ssl_connect())

In the future we may expand the values to include AUTO which would ignore any 
RFC 1918 IP addresses returned by the PASV command.

The only thing to note is that the call to ftp_set_option() must be made before 
ftp_pasv() is called.