revisions to New York Aurora headnote

I've made two small changes to the New York Aurora headnote, based on suggestions from Ken and Susan:

1. In the first sentence, the phrase "preoccupation on" has been changed to "preoccupation with."
2. The last sentence has been revised from "Whitman published two poems in the Aurora but left his position as editor by mid-May, following disagreements with the publishers over their efforts to control his editorials and articles" to "Whitman published two poems in the Aurora but left his position as editor by mid-May, following disagreements with the publishers over their efforts to shape his editorials."

~Liz