jquery.suggestions: Use body width instead of full document width

When there is a overflowing element in the content, the width of
the "document" is wider than the visible width within the browser
window. Use <body> instead of document.

This reverts 4d799b48 (a fix for bug 45668).

Bug: 54091
Bug: 64233
Change-Id: I5268eaf7307159b2eaa4c5749346aa562574a6e2