Does not compile with gcc-6

[olebole]

When compiling with gcc-6 (now standard on Debian testing), I get the following errors:

/build/casasynthesis-0.1/imageanalysis/IO/ImageFitterResults.cc: In static member function 'static std::vector<casa::String, std::allocator<casa::String> > casa::ImageFi
tterResults::unitPrefixes(casa::Bool)':
/build/casasynthesis-0.1/imageanalysis/IO/ImageFitterResults.cc:278:74: error: ambiguous overload for 'operator=' (operand types are 'std::vector<casa::String, std::allocator<casa::String> >' and 'boost::assign_detail::generic_list<char [2]>')
   _prefixesWithCenti = list_of("T")("G")("M")("k")("")("c")("m")("u")("n");
                                                                          ^
In file included from /usr/include/c++/6/vector:69:0,
                 from /usr/include/casacore/casa/Arrays/IPosition.h:35,
                 from /usr/include/casacore/casa/Quanta/Quantum.tcc:36,
                 from /usr/include/casacore/casa/Quanta/Quantum.h:444,
                 from /build/casasynthesis-0.1/imageanalysis/IO/ImageFitterResults.h:29,
                 from /build/casasynthesis-0.1/imageanalysis/IO/ImageFitterResults.cc:28:
/usr/include/c++/6/bits/vector.tcc:167:5: note: candidate: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = casa::String; _Alloc = std::allocator<casa::String>]
     vector<_Tp, _Alloc>::
     ^~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/6/vector:64:0,
                 from /usr/include/casacore/casa/Arrays/IPosition.h:35,
                 from /usr/include/casacore/casa/Quanta/Quantum.tcc:36,
                 from /usr/include/casacore/casa/Quanta/Quantum.h:444,
                 from /build/casasynthesis-0.1/imageanalysis/IO/ImageFitterResults.h:29,
                 from /build/casasynthesis-0.1/imageanalysis/IO/ImageFitterResults.cc:28:
/usr/include/c++/6/bits/stl_vector.h:450:7: note: candidate: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::vector<_Tp, _Alloc>&&) [with _Tp = casa::String; _Alloc = std::allocator<casa::String>]
       operator=(vector&& __x) noexcept(_Alloc_traits::_S_nothrow_move())
       ^~~~~~~~
/usr/include/c++/6/bits/stl_vector.h:471:7: note: candidate: std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(std::initializer_list<_Tp>) [with _Tp = casa::String; _Alloc = std::allocator<casa::String>]
       operator=(initializer_list<value_type> __l)
       ^~~~~~~~

(and similarly in the following line)