package/siunitx.sty: Bundle siunitx 2.5q

package/siunitx.sty: Bundle siunitx 2.5q

My distribution's version of siunitx (2.2i, distributed as part of
dev-texlive/texlive-science-2011) doesn't play well with LaTeX3:

  $ pdflatex -shell-escape root
  ...
  (/usr/share/texmf-dist/tex/latex/l3packages/l3keys2e/l3keys2e.sty)

  !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
  !
  ! LaTeX error: "kernel/command-not-defined"
  !
  ! Control sequence \tl_replace_all_in:Nnn undefined.
  !
  ! See the LaTeX3 documentation for further information.
  !
  ! For immediate help type H <return>.
  !...............................................

  l.333 ...variant:Nn \tl_replace_all_in:Nnn { NnV }

Work around this by bundling the current version.  Source is at:

  https://github.com/josephwright/siunitx/