global: convert indentation-TABs to spaces

Transformed via this shell code:
t=$'\t'
git ls-files \
  | grep -vE '(^|/)((GNU)?[Mm]akefile|ChangeLog)|\.(am|mk)$' \
  | grep -vE 'tests/pr/|help2man' \
  | xargs grep -lE "^ *$t" \
  | xargs perl -MText::Tabs -ni -le \
    '$m=/^( *\t[ \t]*)(.*)/; print $m ? expand($1) . $2 : $_'

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "gnulib"]
-	path = gnulib
-	url = git://git.sv.gnu.org/gnulib.git
+        path = gnulib
+        url = git://git.sv.gnu.org/gnulib.git