don't use singleton for symbol_table This is the first of a series of changes to make the symbol table a part of the interpreter instead of a global object. These changes also aim to simplify the implementation of symbol table so that it is easier to understand and modify. * Functions now own their scope (workspace) data. * The list of subfunctions is contained in the scope rather than a global list. * symtab.h, symtab.cc (class symbol_table): Don't use singleton pattern. * interpreter.h, interpreter.cc (interpreter::m_symbol_table): New data member. (interpreter::~interpreter): Don't set instance to 0. * interpreter-private.h, interpreter-private.cc (__get_symbol_table__): New function. Change all uses of call_stack to access call_stack object from the interpreter.