Upgrade to petsc 3.4.1

Hi Myles,
Petsc had a version bump, and now [petsc-3.4.tar.gz](http://ftp.mcs.anl.gov/pub/petsc/release-snapshots/petsc-3.4.tar.gz)  points to [petsc-3.4.1.tar.gz](http://ftp.mcs.anl.gov/pub/petsc/release-snapshots/petsc-3.4.1.tar.gz) instead of [petsc-3.4.0.tar.gz](http://ftp.mcs.anl.gov/pub/petsc/release-snapshots/petsc-3.4.0.tar.gz). Petsc seems to build and install fine with these modifications. I'm pretty new to both petsc and AUR though, and haven't tried to build anything against this yet.

An alternative, until 3.4.1 is tested, could be to patch the PKGBUILD to explicitly download ```petsc-3.4.0.tar.gz```, a la [this patch](https://gist.github.com/fmuzf/5760811).

Cheers