saving $IFS in run() not altered for code using it

IFS was modified by run() becoming '\n' and so relying to its bash default
was failing tests.

Also some wrong tests corrected because was relying on this behavior to pass.

Fix #89

test/fixtures/bats/loop_keep_IFS.bats

@@ -0,0 +1,16 @@
+# see issue #89
+loop_func() {
+  local search="none one two tree"
+  local d
+
+  for d in $search ; do
+    echo $d
+  done
+}
+
+@test "loop_func" {
+  run loop_func
+  [[ "${lines[3]}" == 'tree' ]]
+  run loop_func
+  [[ "${lines[2]}" == 'two' ]]
+}