By deleting the function and using GncOptionDbImpl::lookup_string_option directly. It returns a string that we don't have to worry about memory-managing. Also create a new GncOptionDbImpl::set_string_option to replace gnc_option_db_set_string_value.
- removes warnings compiling swig engine ... [ 10%] Generating swig-engine.cpp .../libgnucash/engine/engine-helpers.h:31: Warning 313: Unrecognized extern type "C++". .../libgnucash/engine/gnc-date.h:83: Warning 313: Unrecognized extern type "C++". .../libgnucash/engine/qofquery.h:90: Warning 302: Identifier 'QofQuery' redefined (ignored), .../libgnucash/engine/gnc-option.hpp:55: Warning 302: previous definition of 'QofQuery'. .../libgnucash/engine/gnc-commodity.h:56: Warning 313: Unrecognized extern type "C++". .../libgnucash/engine/gncBusiness.h:40: Warning 313: Unrecognized extern type "C++". .../libgnucash/engine/gncEntry.h:37: Warning 313: Unrecognized extern type "C++".
Options is required for book options that are stored as part of the data file and so belongs in engine.