add missing popt dependency for pscomp, fix psmpi2 patch file, style fixes

@carsten-clauss: please review and merge this, so it gets included in https://github.com/hpcugent/easybuild-easyconfigs/pull/759

This resolves part of the problems I'm seeing on my end, but one remains:

```
== FAILED: Installation ended unsuccessfully (build directory: /tmp/easybuild_build/psmpi2/5.0.29/GCC-4.8.2): build failed (first 300 chars): EasyBuild crashed with an error (at easybuild/tools/run.py:382 in parse_cmd_output): cmd " make install " exited with exitcode 2 and output:
No .git or .svn found
make -C mpich2 install
```