PR Summary

This PR fixes the 'always reinstall and restore on fail issue' of Issue #498, and also updates the build version to the next release (beta12). This PR also includes some general code clean up.

PR Context

Install-PSResource was always reinstalling modules even though -Reinstall switch was not selected. This is because the code was not correctly removing 'already installed' packages from the 'toinstall' list.

Also, if a reinstall fails because one of the files is locked (as can happen with loaded .NET binaries) then an error message is emitted and the original resource module files are restored.

Unused variables and parameter arguments were removed.
Some minor code refactoring and method renaming for better clarity.
Added some code regions where they were missing.
Alphabetized using statements per code style guidelines.
Upped module version to 3.0.12 beta.

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