Added ability to execute native powershell scripts

by specifying "#ps1_native", powershell will be launched from the
sysnative file system redirected folder. useful when trying to import
modules that only reside in 64bit powershell (ServerManager for example)
Changes as requested for pep8 + others.

Modified code to be pep8 compliant. Added check for sysnative folder
presence.
Merge pull request #9 from s7oneyuk/master

Added ability to launch 64bit powershell scripts