Another lyxstring error with dec cxx

[Jean-Marc Lasgouttes]

Now that Lars decided to use string::clear() (which dec cxx does not
have), I am forced to compile lyxstring with dec cxx. However, it
breaks with errors like:

cxx: Error: ../../../lyx-devel/src/insets/figinset.C, line 1226: more than
          one operator "+" matches these operands:
            function "operator+(const lyxstring &, lyxstring::value_type)"
            function "lyxstring::operator+(int)"
            operand types are: string + char
        file += cmd + ' ';
--------------------^

How can I avoid this?

JMarc