TempURL: Fixed bug with \r or \n in disposition.

If an object had a \r or \n in its name, it would end up creating an
invalid HTTP Content-Disposition header. Reviewer consensus was to use
URL encoding.

Fixes bug 1306250

Change-Id: Ibccaaed5152b4d09d6aee4966a1982cc0a0da07d
Merge "TempURL: Fixed bug with \r or \n in disposition."