fix glitch in fft.c and add scripts to display data sets without temp file

- usrp/doall: new script to directly evaluate and plot data sets
- usrp/fft.c (fft_complex): don't square the magnitude
- usrp/plscan: if an argument name has the form title=name, use "name" as
  the file name and "title" as the title

usrp/doall

@@ -0,0 +1,11 @@
+#!/bin/bash -x
+opts=
+while [ "$2" ]; do
+    opts="$opts $1"
+    shift
+done
+a=
+for n in $1; do
+    a="$a `basename $n`=<(./evscan $n)"
+done
+eval ./plscan $opts $a