Prevent a class' or namespace's associated free functions

(a "free-function-group" element inside a "class" or "namespace" element)
from reappearing in the synopsis of nested classes or namespaces.
This is a merge of revision 45297 from the boost_docs sandbox.



[SVN r45298]

tools/boostbook

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-Subproject commit f0c7c3d9b9b42c5ef36c308b84ce91c17770f772
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