[aur-general] Merge requests: mpich2 -> mpich

[Jed Brown]

With the release of MPICH 3.0, the project name has been changed from
MPICH2 to MPICH. (It is still backward-compatible.) I have updated my
packages accordingly, which includes a directory change from /opt/mpich2/
to /opt/mpich/.

Could you please merge the following packages?

mpich2 -> mpich
https://aur.archlinux.org/packages/mpich2/
https://aur.archlinux.org/packages/mpich/

parmetis-mpich2 -> parmetis-mpich
https://aur.archlinux.org/packages/parmetis-mpich2/
https://aur.archlinux.org/packages/parmetis-mpich/

ptscotch-mpich2 -> ptscotch-mpich
https://aur.archlinux.org/packages/ptscotch-mpich2/
https://aur.archlinux.org/packages/ptscotch-mpich/