JRUBY-4717: Import digest.rb from CRuby stdlib.

I broke digest lib for 1.8 at 51bf9d9 and Nick fixed it at 288ef4a.
And this is a new try for re-fixing digest library for JRUBY-4717.

 * Update tool/globals_1_8_7.rb to import digest.rb for 1.8 as same as
   1.9.
 * Remove Java implementation of Digest.const_missing. It's defined in
   lib/digest.rb for both 1.8 and 1.9.
 * Revert 288ef1ae. It does not mean that 288ef4a is wrong. It's
   51bf9d9 which should be fixed and needs above fixes. 288ef4a was
   needed.

With importing lib/digest.rb for 1.8 mode, Digest function start working
for 1.8 as same as CRuby.

% ruby187 -rdigest -e 'p Digest("SHA2")'
Digest::SHA2

% jruby -rdigest -e 'p Digest("SHA2")'
Digest::SHA2

% jruby163 -rdigest -e 'p Digest("SHA2")'
NoMethodError: undefined method `Digest' for main:Object
  (root) at -e:1

lib/ruby/1.8/digest.rb

@@ -0,0 +1,50 @@
+require 'digest.so'
+
+module Digest
+  def self.const_missing(name)
+    case name
+    when :SHA256, :SHA384, :SHA512
+      lib = 'digest/sha2.so'
+    else
+      lib = File.join('digest', name.to_s.downcase)
+    end
+
+    begin
+      require lib
+    rescue LoadError => e
+      raise LoadError, "library not found for class Digest::#{name} -- #{lib}", caller(1)
+    end
+    unless Digest.const_defined?(name)
+      raise NameError, "uninitialized constant Digest::#{name}", caller(1)
+    end
+    Digest.const_get(name)
+  end
+
+  class ::Digest::Class
+    # creates a digest object and reads a given file, _name_.
+    # 
+    #  p Digest::SHA256.file("X11R6.8.2-src.tar.bz2").hexdigest
+    #  # => "f02e3c85572dc9ad7cb77c2a638e3be24cc1b5bea9fdbb0b0299c9668475c534"
+    def self.file(name)
+      new.file(name)
+    end
+  end
+
+  module Instance
+    # updates the digest with the contents of a given file _name_ and
+    # returns self.
+    def file(name)
+      File.open(name, "rb") {|f|
+        buf = ""
+        while f.read(16384, buf)
+          update buf
+        end
+      }
+      self
+    end
+  end
+end
+
+def Digest(name)
+  Digest.const_get(name)
+end

src/org/jruby/Ruby.java

@@ -1440,12 +1440,7 @@ private void initBuiltins() {
         addLazyBuiltin("readline.jar", "readline", "org.jruby.ext.ReadlineService");
         addLazyBuiltin("thread.jar", "thread", "org.jruby.libraries.ThreadLibrary");
         addLazyBuiltin("thread.rb", "thread", "org.jruby.libraries.ThreadLibrary");
-        if (is1_9()) { // JRUBY-4717: for 1.9 we should use methods in 1.9/digest.rb
-            addLazyBuiltin("digest.jar", "digest.so", "org.jruby.libraries.DigestLibrary");
-        } else {
-            addLazyBuiltin("digest.jar", "digest", "org.jruby.libraries.DigestLibrary");
-            addLazyBuiltin("digest.rb", "digest", "org.jruby.libraries.DigestLibrary");
-        }
+        addLazyBuiltin("digest.jar", "digest.so", "org.jruby.libraries.DigestLibrary");
         addLazyBuiltin("digest/md5.jar", "digest/md5", "org.jruby.libraries.MD5");
         addLazyBuiltin("digest/rmd160.jar", "digest/rmd160", "org.jruby.libraries.RMD160");
         addLazyBuiltin("digest/sha1.jar", "digest/sha1", "org.jruby.libraries.SHA1");

src/org/jruby/RubyDigest.java

@@ -122,26 +122,6 @@ public static IRubyObject s_hexencode(IRubyObject recv, IRubyObject arg) {
         return toHexString(recv.getRuntime(), arg.convertToString().getBytes());
     }
 
-    @JRubyMethod(name = "const_missing", required = 1, module = true)
-    public static IRubyObject const_missing(ThreadContext ctx, IRubyObject recv, IRubyObject symbol) {
-        Ruby runtime = ctx.getRuntime();
-        String sym = ((RubySymbol)symbol).asJavaString();
-        String libName;
-        if("SHA256".equals(sym) || "SHA384".equals(sym) || "SHA512".equals(sym)) {
-            libName = "digest/sha2.jar";
-        }
-        else {
-            libName = "digest/" + sym.toLowerCase();
-        }
-
-        runtime.getLoadService().require(libName);
-        RubyModule digest = runtime.getModule("Digest");
-        if(!digest.hasConstant(sym)) {
-            throw runtime.newNameError("unitialized constant Digest::" + sym, "Digest::" + sym);
-        }
-        return digest.getConstant(sym);
-    }
-
 
     private static class Metadata {
 

tool/globals_1_8_7.rb

@@ -103,6 +103,7 @@
   'ext/pty/lib/expect.rb' => 'expect.rb',
   'ext/io/wait/lib/nonblock.rb' => 'io/nonblock.rb',
   'ext/nkf/lib/kconv.rb' => 'kconv.rb',
+  'ext/digest/lib/digest.rb' => 'digest.rb',
   'ext/digest/lib/md5.rb' => 'md5.rb',
   'ext/digest/lib/sha1.rb' => 'sha1.rb',
   'ext/digest/sha2/lib/sha2.rb' => 'digest/sha2.rb',