Fixed a bunch of compilation errors when JSON_HAS_INT64 is set.

diff --git a/include/json/value.h b/include/json/value.h
index 32e3455..e3869e5 100644
--- a/include/json/value.h
+++ b/include/json/value.h
@@ -151,12 +151,14 @@
       /// Maximum unsigned int value that can be stored in a Json::Value.
       static const UInt maxUInt;
 
+# if defined(JSON_HAS_INT64)
       /// Minimum signed 64 bits int value that can be stored in a Json::Value.
       static const Int64 minInt64;
       /// Maximum signed 64 bits int value that can be stored in a Json::Value.
       static const Int64 maxInt64;
       /// Maximum unsigned 64 bits int value that can be stored in a Json::Value.
       static const UInt64 maxUInt64;
+#endif // defined(JSON_HAS_INT64)
 
    private:
 #ifndef JSONCPP_DOC_EXCLUDE_IMPLEMENTATION
@@ -265,8 +267,10 @@
 # endif
       Int asInt() const;
       UInt asUInt() const;
+#if defined(JSON_HAS_INT64)
       Int64 asInt64() const;
       UInt64 asUInt64() const;
+#endif // if defined(JSON_HAS_INT64)
       LargestInt asLargestInt() const;
       LargestUInt asLargestUInt() const;
       float asFloat() const;