[Rd] Uninstall registry key the same for all versions (PR#10746)

[Gerhard.Thallinger at tugraz.at]

Full_Name: Gerhard Thallinger
Version: R 2.2.0 through R 2.6.2
OS: Windows XP
Submission from: (NULL) (129.27.145.220)


The uninstall key in the Windows Registry
(HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\) 
is the same ("R for Windows_is1") for all R versions 
(at least from 2.2.0 to 2.6.2). 

This prohibits managing multiple R versions in a clean way, since 
the installation of a new R versions overwrites the uninstall key
of the previous installed version. This makes an uninstall of
a previous version via "Add/Remove Software" impossible.

The uninstall key should also contain the R version number 
(e.g. "R for Windows 2.6.2_is1"). The name of the registry key can 
be set in the Inno Setup definition file using the "AppId" directive.
At the moment "AppId" is not set, therefor "AppName" is used as the
key name.