Use proper page of any PDF figure.

We use the `pdfseparate` utility, found in the `poppler-utils` package,
in order to separate out the pages of the PDF so that we can pass the
right one to XeLaTeX.

Change-Id: I5fdc83c5f5be0d85313ae9fce85c111590a46a5e
Merge "Use proper page of any PDF figure."