Build updates for Fedora 21.

This adds fc21 and removes fc19 from the 2.6 build. There are also two small
specfile fixes.
The behavior of `popd` changed in Bash 4.3 (which is what F21 has).

From the [bash 4.3 release notes](https://lists.gnu.org/archive/html/info-gnu/2014-02/msg00010.html):
```
ff. The `popd' builtin now treats additional arguments as errors.
```
The way I was using it before was wrong  but would not raise an error. I probably copy/pasted the line from elsewhere and didn't remove the extraneous argument.