return a useful value from InflaterInputStream.available

Note the following excerpt from PNGFileFormat.java in SWT:

     /*
     * InflaterInputStream does not consume all bytes in the stream
     * when it is closed. This may leave unread IDAT chunks. The fix
     * is to read all available bytes before closing it.
     */
     while (stream.available() > 0) stream.read();
     stream.close();

This code relies on the documented behavior of
InflaterInputStream.available, which must return "0 after EOF has been
reached, otherwise always return 1".  This is unlike
InputStream.available, which is documented to return "the number of
bytes that can be read (or skipped over) from this input stream
without blocking by the next caller of a method for this input
stream", and says nothing about how many bytes are left until the end
of stream.

This commit modifies InflaterInputStream.available to behave according
to Sun's documentation.

classpath/java/io/BufferedInputStream.java

@@ -72,6 +72,10 @@ public class BufferedInputStream extends InputStream {
     return count;
   }
 
+  public int available() throws IOException {
+    return in.available() + (limit - position);
+  }
+
   public void close() throws IOException {
     in.close();
   }

classpath/java/util/zip/InflaterInputStream.java

@@ -61,6 +61,8 @@ public class InflaterInputStream extends InputStream {
           return count;
         } else if (inflater.needsDictionary()) {
           throw new IOException("missing dictionary");
+        } else if (inflater.finished()) {
+          return -1;
         }
       } catch (DataFormatException e) {
         throw new IOException(e);
@@ -68,6 +70,10 @@ public class InflaterInputStream extends InputStream {
     }
   }
 
+  public int available() throws IOException {
+    return inflater.finished() ? 0 : 1;
+  }
+
   public void close() throws IOException {
     in.close();
     inflater.dispose();