port sync should open only a single rsync connection

[ryandesign (Ryan Carsten Schmidt)]

In src/macports1.0/macports.tcl, MacPorts currently opens a second connection to the rsync server to download the platform-specific PortIndex, and a third connection to download PortIndex.rmd160. Besides being slower and using more network bandwidth and server resources, this presents an opportunity for the user to get a mismatched set of files -- for example, an old PortIndex and a new PortIndex.rmd160 that does not match it.

MacPorts should open one and only one connection to the rsync server when instructed via sudo port sync so to do.