FR (Cache): Add a patch directory (for broken .nupkgs)

[anonhostpi]

It appears that it is possible for broken .nupkgs to exist on NuGet:

• FR (Performance): Refactor and replace TempPath with a native cache path #49 (comment)
• Install-Package failed because a temp file already exists  OneGet/oneget#544

It may be worth adding a -Patch parameter that overrides the current CachePath behavior.

Currently, CachePath is designed to respect and prioritize PackageManagement's package cache over Import-Package's.

However, due to the aforementioned broken packages, it appears to that a -Patch parameter may be warranted.

To implement such an option, all 3 package types need to be addressed.

• The easiest is -Path packages. These would simply need to be redirected to a folder other than CachePath
• The next easiest is likely the Managed-Object packages. These would need to be cloned from PackageManagement's cache to the new -Patch cache
• The most difficult is the standard Managed package. These packages could be sourced out of either cache.
  • In order to avoid cache conflicts, the -Patch parameter will ignore the existing cache. To accomplish this:
    • The -Offline flag will throw an error for SemVer2 packages
    • The -Offline flag will be respected if the package is found in PM's cache
    • For cached packages provided via -Path, these will need to be cached separately

The -Patch parameter should implement a validateset attribute, where the options are Import and SkipImport. This will allow Import-Package to prep the package without prematurely loading it.