Call POSIX::setsid() as a function

[atoomic]

This is avoiding a warning when load with strict sub enabled:

Bareword "POSIX::setsid" not allowed while "strict subs" in use

[Grinnz]

If you are encountering this error, then the function will not work. What system does not have POSIX::setsid defined?

[atoomic]

The problem is not POSIX::setid being defined or not. This is a warning when load with strict subs that I can fix on my side when applying this patch. This probably indicates another issue but was considering using parens to call the function a good thing.
If you disagree let's close this PR.

[Grinnz]

This is certainly an indication of another issue. There should be no case in which the POSIX::setsid symbol is undefined in the parser.

[toddr]

This is certainly an indication of another issue. There should be no case in which the POSIX::setsid symbol is undefined in the parser.

Can't we just merge it as "more legible code?"