Please report errors from the library instead of exit()-ing

[rbalint]

The default error handler now exits which is not ideal for a shared library:

void                                                                                                                                    
error_default(const char *msg, ...)                                                                                                     
{                                                                                                                                       
  va_list args;                                                                                                                         
                                                                                                                                        
  va_start(args, msg);                                                                                                                  
  vfprintf(stderr, msg, args);                                                                                                          
  va_end(args);                                                                                                                         
  exit(EXIT_FAILURE);                                                                                                                   
}

Other parts of the code assume that when errors are reported the execution of the code stops. This may allow memory corruption when the error handler is replaced with something that does not exit().