Removed further timing differences during SSL message decryption in ssl_decrypt_buf()

New padding checking is unbiased on correct or incorrect padding and
has no branch prediction timing differences.

The additional MAC checks further straighten out the timing differences.
diff --git a/ChangeLog b/ChangeLog
index a4c11f6..75989bb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -4,6 +4,10 @@
 Bugfix
    * Fixed memory leak in ssl_free() and ssl_reset() for active session
 
+Security
+   * Removed further timing differences during SSL message decryption in
+     ssl_decrypt_buf()
+
 = Version 1.2.5 released 2013-02-02
 Changes
    * Allow enabling of dummy error_strerror() to support some use-cases