Don't lose current line # context e.g. in Source vs. Blame

[raould]

(a) load a repo in gitx-dev (b) View > Tree View (c) pick a long file to see the Source of (d) scroll down some, more than one page of text (e) click on the Blame button to switch to that view (f) Expected: blame will show me the blame around the line i'm already looking at / Actual: it jumps back to line 1, losing my context.