allow iedit-rectangle-mode to take beg end programatically

- also add warning when no region is selected.
fix tests to call iedit-rectangle-mode interactively
set `iedit-rectangle` to the actual rectangle corners

- after inserting necessary spaces to pad out full rectangle
refactor out common test code in "test-util"
use real buffer for testing to ease debugging
add test to ensure padding of EOL happens to make up rectangle
Move iedit-apply-global-modification to iedit
Follow error convention
Merge branch 'redo-prs' of github.com:lewang/iedit

Conflicts:
	iedit-rect.el
	iedit-tests.el
Remove test-util.el