Lots of bad TAB eliminations.

I started from tabs that are not on the beginning of lines, and in
several places I did further cleanings.

If you're worried about knowing who wrote some code, for example, if you
get to this commit in "git blame", then note that you can use the "-w"
flag in many git commands to ignore whitespaces.  For example, to see
per-line authors, use "git blame -w <file>".  Another example: to see
the (*much* smaller) non-whitespace changes in this (or any other)
commit, use "git log -p -w -1 <sha1>".

original commit: 672910f27b856549ad08d38832b6714edf226c8e

collects/schemeunit/gui.rkt

@@ -1,3 +1,3 @@
-#lang racket
+#lang racket/base
 (require rackunit/gui)
 (provide (all-from-out rackunit/gui))

collects/schemeunit/text-ui.rkt

@@ -1,3 +1,3 @@
-#lang racket
+#lang racket/base
 (require rackunit/text-ui)
 (provide (all-from-out rackunit/text-ui))