Skip link detection in Windows

[aivarannamaa]

If p is a Serial over Bluetooth link, then os.path.islink(p) may take several seconds.

In two of my Windows 10 computers following code used to take 5 seconds:

from serial.tools.list_ports import comports
for p in comports():
    print(p)

I found out that the delay was caused by os.path.islink('COM5'). COM5 is one of the "Bluetooth over serial" ports backed by LogiLink Bluetooth dongle.

After my change it takes 0.01 seconds.

If I'm not mistaken, then list_ports_windows can't list symlinks anyway, so this time consuming check can be turned off for Windows.

[zsquareplusc]

Right, that could be skipped.

What I do not like is that this introduces a new method to check for the platform and makes that module platform dependent too. I guess it easier to add a parameter to the ListPortInfo constructor. I've implemented that.