[LinuxCNC/linuxcnc Issue#653] twopass not loading userspace component with serial port as an argument

Here are the steps I follow to reproduce the issue:

1. in ini file:
TWOPASS = ON
HALFILE = plasmac.tcl

2. in plasmac.tcl:
loadusr -Wn pmx485 ./pmx485.py /dev/ttyS0

This is what I expected to happen:

The component to load with /dev/ttyS0 passed as an argument

This is what happened instead:

The following messages in the terminal:
Starting LinuxCNC…
twopass:invoked with <> options
twopass:found ./machine.hal
twopass:found ./plasmac.tcl
twopass:found ./axismetricconnections.hal
twopass:pass0: loadusr -Wn pmx485 ./pmx485.py /dev/ttyS0
twopass:loadusr not executable

It worked properly:

* before commit 1900782
* without twopass
*. in 2.8

Information about my hardware and software:

* I am using Debian GNU/Linux 9.11 (stretch)
* I am using 4.9.0-9-rt-amd64
* I am running a RIP build
* I am using 2.9.0~pre0.700.g1337f284e
* I am using AXIS
* I am using a sim

pmx485 is a component that uses PyModbus to communicate with a Modbus ASCII peripheral.