Nicholas' patches.
Merge branch 'reflow_nicholas_patches' into reflow_merge_nicholas_patches
Revert "Add reflow flag (-F) to resize-pane."

This reverts commit 596e8b7f952dd782bb5e57be609e5f26dbc2847a.
This is going to become the default behavior, so no special options needed.
Remove reflow window option; now reflowing happens all the time.
Refactor to do reflowing from screen_resize().