Add install files to the build

[matt335672]

Adds installation files to the build.

make install now also creates the following files:-

• /usr/libexec/pulseaudio-module-xrdp/load_pa_modules.sh which dynamically loads the xrdp pulseaudio modules
• /etc/xdg/autostart/pulseaudio-xrdp.desktop which calls to the above for any desktop which supports the XDG autostart specification.

This PR is dependent on #59

This method of loading pulseaudio drivers is compatible with existing systems, and removes the need for PA_SCRIPT to be set in /etc/xrdp/sesman.ini for all systems.

[matt335672]

@metalefty - I'm aware you've approved this, but related to your comment above I've added an extra command line switch to configure to make FreeBSD easier to support.

The following now works for me on FreeBSD 13.0:-

./bootstrap
CFLAGS="-I/usr/local/include" ./configure \
    --with-xdgautostart-dir=/usr/local/etc/xdg/autostart \
    PULSE_DIR=/usr/ports/audio/pulseaudio/work/pulseaudio-13.0
make
sudo make install

If you're happy with this, I'll start merging in the other changes to devel.

[metalefty]

@matt335672 Thanks, I'm fine with that.

[metalefty]

Happy if we can avoid this hardcoded path of pactl.

[matt335672]

Good point - this will be broken on FreeBSD of course.

I'll assume it's in the PATH. It's not a privileged script, and if the pa utils aren't in the PATH for the desktop, the user will have other problems anyway.

[matt335672]

I'll look into this a bit further - my FreeBSD testing was OK, so something's happening here I'm not expecting

[matt335672]

Got it - under FreeBSD, the PULSE_SCRIPT environment variable is loading the xrdp drivers. The load_pa_modules.sh fails, but that doesn't matter.

Removing the PULSE_SCRIPT definition is causing some problems. I'll get this working on FreeBSD, re-test on a couple of Linuxes and then post an updated script for re-review.

[matt335672]

Script now works OK with my FreeBSD 13 testing, with or without the PULSE_SCRIPT setting.

A further change was required in that on my FreeBSD VM without PULSE_SCRIPT set, the pulseaudio daemon was using the built-in sound card (oss_output.dsp0) rather than the xrdp channel. I've now set the default source and sink to be the xrdp devices if we're in an xrdp session. I can't think of any reason why the user wouldn't want to do this anyway.

I've also retested on Ubuntu 20.04, Ubuntu 18.04, Debian Buster and CentOS 8 with or without the PULSE_SCRIPT setting. They all seem OK, so that leaves the way open to removing that setting in a later version of xrdp.