PowerShell v2/3 caches the output stream. Then it throws errors due to
the FileStream not being what is expected. Fixes "The OS handle's
position is not what FileStream expected. Do not use a handle
simultaneously in one FileStream and in Win32 code or another
FileStream."

The fix comes from
http://www.leeholmes.com/blog/2008/07/30/workaround-the-os-handles-position-is-not-what-filestream-expected/
plus information in the comments that actually makes it work.

The Chocolatey install PowerShell script has been signed
at dot org and all of the scripts in Chocolatey 0.9.10 are
being signed, so it is appropriate to sign this script as
well for the benefit of folks who would need that.

The output from error messages is way too much when these are on by
default. It would be helpful to see only what has errored and allow the
user to investigate further if need be. This gives the user the ability
to choose whether or not to add those values to the arguments as part
of `install_options` and `uninstall_options`.

To increase awareness that Professional and Business editions are
available, add information in the readme.

There is a syntax error in the readme related to setting the default
provider for Windows. It needs a second set of brackets surrounding
Package.

If the PowerShell Output redirection fix does not successfully apply,
we don't want it to fail the entire script. It uses internal variables
that only apply to the PowerShell InternalHost/ConsoleHost that
short-circuited logging and caused a FileStream error when you
attempted to write to multiple log streams.

Due to sometimes calling this script with non-default PowerShell
hosts (like with the new 2.0 puppet powershell provider), we want to
ensure that if the fix errors, it does not fail the entire script.