Test update

Updated tests for new desired behavior.  All usages of -CertificateThumbprint parameters have been replaced with just -Certificate, and there's a new test to make sure that file system paths or cert:\ paths (including relative paths) can also be used.
Updated Protect-Data -Certificate parameter
Updated -Certificate parameter of Unprotect-Data
Code updates complete; tests passing

Still need to add deprecated warnings for CertificateThumbprint parameter, and update documentation
Updated help and added warnings to old Thumbprint parameters

Also moved the deprecated parameters to later positions in the param blocks, so tab completion will find the preferred parameters first.
Performance increase

Certificate provider is slow, particularly on PowerShell v2.  Avoiding calls to GetCertificateByThumbprint wherever possible is beneficial here.
Merge pull request #8 from dlwyatt/CertificateParameterCleanup

Certificate parameter cleanup