Display clear table of updated Refs

Supply before & after in an ascii table...
Tweak dirt-report appearance

Commit Tree-Dirt History
------------------------

	Earliest                                              Latest
	|                                                          |
	......................DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD

	D = dirty commits (file tree fixed)
	m = modified commits (commit message or parents changed)
	. = clean commits (no changes to file tree)

	                        Before     After
	-------------------------------------------
	First modified commit | 0812460e | bce5bbae
	Last dirty commit     | 57050032 | afeb9d90

Updating 1 Ref
--------------

	Ref                 Before     After
	---------------------------------------
	refs/heads/master | cdf24c1c | ba13b47a