When Doxygen option INLINE_INHERITED_MEMB=YES is used, Doxygen generates
duplicate class member definitions with the same ids, when the member is
inherited from a base class. This results in duplicate ids in BoostBook output
and the corresponding errors.
Work around this by checking if the member id starts with the id of the
enclosing class. If it does then the member is assumed to be a genuine member
of the class and we generate a Doxygen id for it. Doxygen refs will point to
this definition of the member. If the member id is different then it must be
an inherited member, and we don't generate a Doxygen id for it. BoostBook
stylesheets will generate a unique id for it, which will be used to link
synopsis to reference of the member in the derived class' documentation.