Add support for installation directly via HTTP.
While we're here, remove the menu-item for Passive FTP (since moving to
ftp(1) and switching FTPMODE to `auto' by default -- see r251613 -- the
single remaining FTP menu-item works for both ftp.f.o and ftp-archive.f.o;
previously each requiring separately active versus passive both work with
the `auto' setting). In scripting you still have mediaSetFTPActive and
mediaSetFTPPassive but the remaining FTP menu-item uses mediaSetFTP which
defaults to `auto' (aforementioned SVN r251613).