copy va_list because vsyslog consumes
Add new switch argument of logging_type

This option controls log output destination by
specifing comma separated names.
Valid names are syslog, file and stdout.
Without this option, the behavior does not change.

Example:
```
switch -t syslog,file,stdout -l debug
```
Merge pull request #87 from iHiroakiKawai/log_type

make switch log output destination configurable