- Move `ExpandInstallerPath()` from userinit.c to livecd.c, and update
its SAL2 annotations and Doxygen comment.
- Make `StartInstaller()` directly use the cached ReactOS installer path.
- This avoids invoking yet again `ExpandInstallerPath()` when trying to
locate the installer also for the aim of determining whether to disable
the "Install" button.
- Transform TryToStartShell() into a StartProcess() function whose aim
is just to start processes, since there is no extra initialization needed
for starting a shell process.
- Modify StartInstaller() to call StartProcess() for starting the ReactOS GUI
installer found on the installation media, from a path automatically expanded
depending on the ambient CPU architecture.
svn path=/branches/setup_improvements/; revision=75331