release 0.12.3

This release comes exactly 1 year and 1 day after the previous
release, for which the inspiration was this quote:

    Arrakis teaches the attitude of the knife -- chopping off
    what's incomplete and saying: "Now, it's complete because
    it's ended here."

CHANGELOG.md

@@ -1,5 +1,5 @@
-v0.12.3 (unreleased)
-----------------------
+v0.12.3 (2016-01-20)
+--------------------
 * **[qt]** upgrade the patched Qt to the last Qt 4.8 commit
 * removed support for CentOS 5 builds
 * update OpenSSL to 1.0.2e and xz to 5.2.2 and libjpeg to 9b

VERSION

@@ -1 +1 @@
-0.12.3-dev
+0.12.3