Remove an outdated comment

According to Stephen there are two reasons the ioservice continues to run:

* The listener is always listening
* The scheduler is always scheduling

This is the science.
Don't force Linux

FREEDM might compile on other Unixes so there is no point in failing them
arbitrarily.
cmake: close conditionals with empty parens

This is a common CMake coding standard (e.g. mandated by KDE) which
makes the code slightly cleaner
cmake: alphabetize options
Merge branch 'PlugNPlay' of github.com:scj7t4/FREEDM into PlugNPlay