tests: test experimental.spacemovesdown config for commit -i

The feature is still very experimental, but at least its behavior is captured
in the test.

tests/test-commit-interactive-curses.t

@@ -318,6 +318,25 b' reflect this edition.'
   foo
   hello world
   lower
+
+Check spacemovesdown
+
+  $ cat <<EOF >> $HGRCPATH
+  > [experimental]
+  > spacemovesdown = true
+  > EOF
+  $ cat <<EOF >testModeCommands
+  > TOGGLE
+  > TOGGLE
+  > X
+  > EOF
+  $ hg status -q
+  M b
+  M x
+  $ hg commit -i -m "nothing to commit?" -d "0 0"
+  no changes to record
+  [1]
+
 Check ui.interface logic for the chunkselector
 
 The default interface is text