Better device detection on Linux, Unix

[tresf]

Quoting an upstream bug report which originally identified this issue:

JSSC, on unix based systems like linux and MacOSX, when listing serial ports
tries to open each port to ensure its existence. While this check works well for
linux ports /dev/ttyS0..31, it leads to unexpected behaviors on MacOSX in
particular with USB-CDC virtual serial ports.

This patch disable the check and keep it enabled only for linux ttySxx ports.

This adds also tty.* and cu.* to the list of available serial ports on MacOSX.

Using a hypervisor I tested adding a "physical" port to macOS and can confirm that /dev/cu.* is correct.

@GMKennedy is running some additional tests.

Supersedes #64.
Related scream3r#120
Related scream3r#92

[tresf]

@GMKennedy says this tests well and is good to merge.