problem installing latest (and older) Macports

[John Graybeal]

I'm trying to install macports on my Mac (which has a long history).  (/opt/local/bin/port is dated 2005.12.15; running 'sudo port selfupdate' gives 
 can't find package darwinports  while executing  "package require darwinports" (file "/opt/local/bin/port" line 41)    
)

Installing the Mountain Lion pkg gives "Your existing MacPorts or DarwinPorts installation is too old to be upgraded by this installer. Please install MacPorts 1.7.1 first."   Renaming port and portindex doesn't change this; not sure how to get rid of my ancient install.

After downloading 1.7.1, I am mystified as to what to do to install it. 

I don't think I care about my old MacPorts installation, I just want a current one.

John

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John Graybeal