add some documents [ci skip]

* bignum.c (Init_Bignum): [DOC] Bignum::GMP_VERSION.

* complex.c (Init_Complex): [DOC] ignore an internal class.

* dir.c (Init_Dir): [DOC] File::FNM_SYSCASE.

* file.c (rb_file_exists_p): [DOC] File.exists? is deprecated.

* object.c (rb_mod_initialize_clone): [DOC] ignore implementation
  detail.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46990 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

bignum.c

@@ -7037,6 +7037,7 @@ Init_Bignum(void)
     rb_define_method(rb_cBignum, "even?", rb_big_even_p, 0);
 
 #ifdef USE_GMP
+    /* The version of loaded GMP. */
     rb_define_const(rb_cBignum, "GMP_VERSION", rb_sprintf("GMP %s", gmp_version));
 #endif
 

complex.c

@@ -2167,7 +2167,7 @@ Init_Complex(void)
     rb_define_method(rb_cComplex, "inspect", nucomp_inspect, 0);
 
     rb_define_private_method(rb_cComplex, "marshal_dump", nucomp_marshal_dump, 0);
-    compat = rb_define_class_under(rb_cComplex, "compatible", rb_cObject);
+    compat = rb_define_class_under(rb_cComplex, "compatible", rb_cObject); /* :nodoc: */
     rb_define_private_method(compat, "marshal_load", nucomp_marshal_load, 1);
     rb_marshal_define_compat(rb_cComplex, compat, nucomp_dumper, nucomp_loader);
 

dir.c

@@ -2316,5 +2316,11 @@ Init_Dir(void)
      *  Allows file globbing through "{a,b}" in File.fnmatch patterns.
      */
     rb_file_const("FNM_EXTGLOB", INT2FIX(FNM_EXTGLOB));
+
+    /*  Document-const: File::Constants::FNM_SYSCASE
+     *
+     *  System default case insensitiveness, equals to FNM_CASEFOLD or
+     *  0.
+     */
     rb_file_const("FNM_SYSCASE", INT2FIX(FNM_SYSCASE));
 }

file.c

@@ -1429,7 +1429,6 @@ rb_file_chardev_p(VALUE obj, VALUE fname)
 /*
  * call-seq:
  *    File.exist?(file_name)    ->  true or false
- *    File.exists?(file_name)   ->  true or false
  *
  * Return <code>true</code> if the named file exists.
  *
@@ -1447,6 +1446,12 @@ rb_file_exist_p(VALUE obj, VALUE fname)
     return Qtrue;
 }
 
+/*
+ * call-seq:
+ *    File.exists?(file_name)   ->  true or false
+ *
+ * Deprecated method. Don't use.
+ */
 static VALUE
 rb_file_exists_p(VALUE obj, VALUE fname)
 {

object.c

@@ -1707,6 +1707,7 @@ rb_mod_initialize(VALUE module)
     return Qnil;
 }
 
+/* :nodoc: */
 static VALUE
 rb_mod_initialize_clone(VALUE clone, VALUE orig)
 {