Ruby/Perl bindings fail to compile with -Werror=format-security

With Fedora 21 the option -Werror=format-security has been enabled. As a result, the code generated by Swig for the Ruby bindings fail to compile. The culprit code is in ruby.i:

rb_raise(merror, mex.what());

Which is using a method from the printf family but is not using a static format string.