Merged in antmerlino/apps/ftp-ipv6 (pull request #122)

FTP: Adds support for IPv6 and fixes various transfer issues

* netutils/ftpd: Fix support for IPv6 FTP server

* netutils/ftpc:Adds support for IPv6 sockets

* ftpc: Must convert port received by EPSV reply to network order

* ftpc: Data socket address for passive connection should be same as server address

* ftpc: Must skip human readable string in EPSV response before scanning for port

* ftpc: Don't send PASS command if USER command was sufficient. ie no password required

* ftpc: Generically handle permanent negative completion in shard ftpc_cmd logic

* ftpc: Minor addresssing fix

* ftpc: Tweak logic for overriding network debugging output

* FTP: Adds option for setting stack size of various threads in FTPD and FTPC

* netutils/ftpd: Fixes build error setting IPv4 address. sin_addr => sin_addr.s_addr

* netutils/ftpd: Protects against partial write returns by looping in that case

Approved-by: Gregory Nutt <gnutt@nuttx.org>