interactions with /usr/local (was: error installing git-core ...)

[Stephen Bannasch]

Reading Ryan's last message. I realized that my problem could be 
interactions with libraries I had already installed into /usr/local 
so I tried this:

$ sudo mv /usr/local /usr/localx
$ sudo port install db44
Library not loaded: /usr/local/lib/libreadline.5.1.dylib
   Referenced from: /opt/local/share/macports/Tcl/pextlib1.0/Pextlib.dylib
   Reason: image not found
     while executing
"load /opt/local/share/macports/Tcl/pextlib1.0/Pextlib.dylib"
     ("package ifneeded" script)
     invoked from within
"package require Pextlib 1.0"
     (procedure "mportinit" line 365)
     invoked from within
"mportinit ui_options global_options global_variations"
Error: /opt/local/bin/port: Failed to initialize MacPorts, Library 
not loaded: /usr/local/lib/libreadline.5.1.dylib
   Referenced from: /opt/local/share/macports/Tcl/pextlib1.0/Pextlib.dylib
   Reason: image not found

Clue ...!

OK ... so a bunch of my ports were probably built using things in 
/usr/local -- and this isn't useful.

Is there a quick way I can tell ports to build everything again?

Is there a better way to have code built from source in /usr/local 
and other code built with ports (that use some libraries in common) 
and not have them interact without temporarily renaming /usr/local?