ChangeLog: "1.5 beta1" --> "1.4.90 (1.5 beta1)"

(for consistency with other beta release headings)
diff --git a/ChangeLog.txt b/ChangeLog.txt
index 68df4c3..29352e4 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -5,8 +5,8 @@
 path" of libjpeg-turbo's Huffman decoder to read from uninitialized memory.
 
 
-1.5 beta1
-=========
+1.4.90 (1.5 beta1)
+==================
 
 [1] Added full SIMD acceleration for PowerPC platforms using AltiVec VMX
 (128-bit SIMD) instructions.  Although the performance of libjpeg-turbo on