debian/ubuntu multiarch dependency checking

Currently RVM uses "dpkg -s" to check if a required library is installed.  When using multiarch, this simple check will fail when you have multiple arch versions of a package installed.  

In my case it was zlib1g.

    # dpkg -s zlib1g
    dpkg-query: error: --status needs a valid package name but 'zlib1g' is not: ambiguous package name 'zlib1g' with more than one installed instance

In order for dpkg -s to report correctly, the machine arch needs to be appended.

    # dpkg -s zlib1g:amd64
        Package: zlib1g
        Status: install ok installed
        .... etc

    # dpkg -s zlib1g:i386
        Package: zlib1g
        Status: install ok installed
        .... etc