Allow pretty printing function decls for internal purposes
    
    It appears that function_decl::get_pretty_representation doesn't make
    the difference between internal and non-internal purposes.  This patch
    fixes that by making the helper
    get_pretty_representation_of_declarator() take an "internal" flag and
    calls that.
    
    	* include/abg-ir.h
    	(function_decl::get_pretty_representation_of_declarator): Take an
    	"internal" flag.
    	* src/abg-ir.cc
    	(function_decl::get_pretty_representation_of_declarator): Take an
    	"internal" flag.
    	(function_decl::get_pretty_representation): Pass the "internal"
    	flag to the function
    	function_decl::get_pretty_representation_of_declarator.
    	(function_decl::parameter::get_type_name):  Better handle variadic
    	parameter type.
    	(function_decl::parameter::get_type_pretty_representation):
    	Likewise.
    
    Signed-off-by: Dodji Seketeli <dodji@redhat.com>