Replace Fixnum with Integer

Fixnum was deprecated in Ruby 2.5 and removed in Ruby 3.2. I'm not
sure this is safe, as it is possible Fixnum was used deliberately
instead of Integer, maybe because the integers were going to be
passed to Tcl/Tk.  However, from a partial review, it looks like
the code was just using Fixnum instead of Integer.  For example,
the lib/tkextlib/iwidgets/notebook.rb change passes non-Fixnum
instances directly to tk_send_without_enc, so the only change
is that large negative integers are now changed to nil instead
of being passed directly.

MANUAL_tcltklib.ja

@@ -135,7 +135,7 @@ require "tcltklib" すると, 以下のモジュール, クラスが利用可能
   メソッド _return_value()
       直前の Tcl_Eval の戻り値を返します. 0(TCL_OK) で正常終了です.
     引数: 無し
-    戻り値 (Fixnum): 直前の Tcl_Eval() が返した値.
+    戻り値 (Integer): 直前の Tcl_Eval() が返した値.
 
 ==============================================================
 

lib/multi-tk.rb

@@ -1279,7 +1279,7 @@ def initialize(master, safeip=true, keys={})
 
     name, safe, safe_opts, tk_opts = _parse_slaveopts(keys)
 
-    safe = 1 if safe && !safe.kind_of?(Fixnum)
+    safe = 1 if safe && !safe.kind_of?(Integer)
 
     @safe_base = false
 

lib/tkextlib/iwidgets/notebook.rb

@@ -150,7 +150,7 @@ def yscrollbar(bar=nil)
   def view(*idxs)
     if idxs.size == 0
       idx = num_or_str(tk_send_without_enc('view'))
-      if idx.kind_of?(Fixnum) && idx < 0
+      if idx.kind_of?(Integer) && idx < 0
         nil
       else
         idx

lib/tkextlib/iwidgets/tabnotebook.rb

@@ -156,7 +156,7 @@ def yscrollbar(bar=nil)
   def view(*index)
     if index.size == 0
       idx = num_or_str(tk_send_without_enc('view'))
-      if idx.kind_of?(Fixnum) && idx < 0
+      if idx.kind_of?(Integer) && idx < 0
         nil
       else
         idx

lib/tkextlib/tcllib/tablelist_core.rb

@@ -482,15 +482,15 @@ def configrows(*args) # args ==> idx, opt, val, idx, opt, val, ...
 
   def containing(y)
     idx = num_or_str(tk_send('containing', y))
-    (idx.kind_of?(Fixnum) && idx < 0)?  nil: idx
+    (idx.kind_of?(Integer) && idx < 0)?  nil: idx
   end
 
   def containing_cell(x, y)
     idx = _from_idx(tk_send('containingcell', x, y))
     if idx.kind_of?(Array)
       [
-        ((idx[0].kind_of?(Fixnum) && idx[0] < 0)?  nil: idx[0]),
-        ((idx[1].kind_of?(Fixnum) && idx[1] < 0)?  nil: idx[1])
+        ((idx[0].kind_of?(Integer) && idx[0] < 0)?  nil: idx[0]),
+        ((idx[1].kind_of?(Integer) && idx[1] < 0)?  nil: idx[1])
       ]
     else
       idx
@@ -500,7 +500,7 @@ def containing_cell(x, y)
 
   def containing_column(x)
     idx = num_or_str(tk_send('containingcolumn', x))
-    (idx.kind_of?(Fixnum) && idx < 0)?  nil: idx
+    (idx.kind_of?(Integer) && idx < 0)?  nil: idx
   end
   alias containingcolumn containing_column
 
@@ -889,7 +889,7 @@ def sort_by_columnlist(idxlist, orderlist=None)
 
   def sortcolumn
     idx = num_or_str(tk_send('sortcolumn'))
-    (idx.kind_of?(Fixnum) && idx < 0)?  nil: idx
+    (idx.kind_of?(Integer) && idx < 0)?  nil: idx
   end
 
   def sortcolumnlist

lib/tkextlib/treectrl/tktreectrl.rb

@@ -1170,7 +1170,7 @@ def item_order(item, visible=false)
       ret = num_or_str(tk_send('item', 'order', item))
     end
 
-    (ret.kind_of?(Fixnum) && ret < 0)? nil: ret
+    (ret.kind_of?(Integer) && ret < 0)? nil: ret
   end
   def item_visible_order(item)
     item_order(item, true)

sample/tktextio.rb

@@ -596,7 +596,7 @@ def printf(*args)
 
   def putc(c)
     _check_writable
-    c = c.chr if c.kind_of?(Fixnum)
+    c = c.chr if c.kind_of?(Integer)
     _write(c)
     c
   end
@@ -854,7 +854,7 @@ def ungetc(c)
     end
 
     _check_readable
-    c = c.chr if c.kind_of?(Fixnum)
+    c = c.chr if c.kind_of?(Integer)
     if compare(@txtpos, '>', '1.0')
       @txtpos.set(@txtpos - '1 char')
       delete(@txtpos)