Detecting NetworkSimplicity in setup.exe

["Max Bowsher" <maxb at ukf dot net>]

I've just installed the latest version of NetworkSimplicity (renaming my
Cygwin registry keys first).

I propose a 3-level system for detecting problematical mount tables:

When NetworkSimplicity is installed, setup can simply look for "OpenSSH on
Windows *" in HKLM\Software\Microsoft\Windows\CurrentVersion\Uninstall\.
In this case, warn the user that Cygwin and NetworkSimplicity are mutually
incompatible (perhaps link to a webpage with a detailed explanation?), and
terminate the install.

As a fallback method, check the mount table mount table with the following
characteristic:
/bin == /ssh == /usr/bin == /usr/lib == /usr/local/bin == /usr/local/etc
This particular odd layout is unique enough to assume that NetworkSimplicity
was installed, but has been uncleanly removed. Therefore display a message
explaining that the mount table is left over from a NetworkSimplicity
install, and offer to either wipe the mount table and recreate it, or exit
setup.

Lastly, as a final contingency, check for /bin == /lib or /usr/bin ==
/usr/lib. In that case, warn, and offer to revert the mount table to Cygwin
defaults, or continue.

Perhaps, when setup is doing an update rather than an initial install,
behaviour should be more relaxed - for example, don't exit setup, just shout
loudly.

Comments requested,

Max.