If you wanted to set a configuration option like
`config:install_tree:root` to "C:/path/to/config.yaml", Spack had
trouble parsing this because of the ":" in the value. This adds
logic to allow using quotes to enclose the value, so you can add
`config:install_tree:root:"C:/path/to/config.yaml"`.
Configuration keys should never contain a quote character, so the
presence of any quote is taken to mean that the rest of the string
is specifying the value.
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