Force switching to 64-bit if running in a 32-bit process on a 64-bit box

[tyrken]

If for some reason you run start Chocolatey from a 32-bit shell or other program, it will run with 32-bit powershell. This causes the Windows File System Redirector to kick up & mess with C:\Windows\System32, the Registry equivalent to shift some reg keys, and the ProgramFile* env vars to change.

This can mess up some chocolateyInstall.ps1 scripts (I only have private examples, but expect others may exist), so for simplicity's sake we should force switching to 64-bit powershell by re-running ourselves with the original command arguments. This would also simplify some internal functionality (e.g. PR #420).