* lukaszmluki/master:
  ftp: add invalid code for RETR operation
  ftp: probe seek capability
  ftp: fix seeking beyond file size
  ftp: abort function optimalization
  ftp: explicit return code checks
  ftp: fix flush control connection input
  ftp: reconnect on tcp read error
Merged-by: Michael Niedermayer <michaelni@gmx.at>