Make MSI custom action debug pop-up more informative

Make MSI custom action debug pop-up more informative

Each MSI custom action pops-up a message box in the _DEBUG version
before commencing execution. This opens a time window for developer to
attach debugger to the msiexec.exe process, set the breakpoints before
custom action proceeds with execution.

While those pop-up dialogs are targeted to a limited audience, they were
very sparse. With this patch, they become more informative and they also
provide PID of the msiexec.exe process to attach debugger to.
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20181112122246.13556-3-simon@rozman.si>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg17907.html

Signed-off-by: Gert Doering <gert@greenie.muc.de>