Werk #8567: Invertible Graphite mangling

When sending performance data to Graphite, the host/service/variable part needs to be mangled. The result of the default mangling is more readable (it simply replaces special characters with an underscore), but it is not invertible. This change adds C-style mangling using the standard octal escapes ('\ooo'), so you can reconstruct the various parts from the data sent to Graphite.

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