Debug Functions for outputing diagnostics. These functions relate to outputing diagnostic messages and information. Use of these functions requires DEBUG to be defined at compilation time. On Unix systems, the configure script has a command-line option --enable-debug. On Win32 a debug configuration exists. Available for use to prevent compiler warnings when a function argument is not used. Sometimes this is unavoidable because function has to conform to an interface. @x: unused function argument that generates compiler warning. When DEBUG is defined this will write a formatted message to the platform defined error stream. The format of the message has the same semantics as standard C library call printf(). The error message displayed is prepended by the process id, the file and the line number, where debug_msg() was called. On Unix the message is rendered on the standard error stream. On Win32 a debug message is created using the Win32 API function OutputDebugString(). @lp: @len: @argv0: