Changes Introduced in 3#6

• toplevel_print_options and debugger_print_options are new Prolog flags controlling the toplevel's and debugger's printing behavior.
• is_mutable/1 is a new built-in which is true for mutables.
• ~@ is a new spec in format/[2,3] for arbitrary goals.
• Mutables are initialized correctly when read in.
• The finite domain constraint solver (library(clpfd)) has been enhanced by a programming interface for global constraints, improved compilation to library constraints and other performance enhancements, and by a number of new exported constraints.
• library(objects): New hook predicate user:method_expansion/3.
• library(sockets): socket_select/5 has extended functionality.
• Efficiency bugs in format/[2,3] fixed.
• Bug in save_program/[1,2] with native code fixed.
• Bugs in library(chr) fixed, and a couple of new constraint handlers fixed.
• A problem with source linked debugging of DCG rules fixed.
• Prevent looping on duplicates in module/2 decl.
• Prevent memory overrun in library(tcltk).