Import-VisualStudioEnvironment.psm1 Fix for 64-Bit Environments

On 64-Bit machines starting a 64-Bit Powershell process the
$versionSearchKey links into the 64-Bit part of the Registry on HKLM.
Because VisualStudio is a 32-Bit Project a "Wow6432Node" Search key is
neccessary.