Multiple configfile-related changes
- Print current configfile in the output of 'env' (this also makes configfile changeable in runtime via 'setenv')
- In 'configfile' commands, print which config file is being used
- Fix behavior of existing 'more_conf'
- Make load_config() return filename and hash, rather than unconditionally overwrite $conf
- Bring back %conf2 into implementation of save_config; it is necessary to be there or 'configfile' is getting lost/deleted in the runtime config
Other changes
- Add 'set' as alias for 'setenv'
- Add unsetenv/unset (opposite of setenv/set)
- Do not print unset/undefined values in 'env'