Do not spawn a child process if setuid fails
Raise an exception if a user in the config file does not exist
Update description of user option in config file
Add changelog notes for user option changes
Prepare 3.0b2 release
Back to -dev until next release
Patch by David Birdsong, adding rlimit caps

This allows to call programs with different rlimits than the ones set by
default. For example, the following options work after this patch:

```
[program:prog1]
command=/bin/cat
minprocs=4096
minfds=4096
stacksize=10240
```