Prepare 1.5.2 release.

ChangeLog

 ChangeLog for Pylint
 --------------------
---
+2015-12-21
+
     * Don't crash if graphviz is not installed, instead emit a
       warning letting the user to know.

pylint/__pkginfo__.py

@@ -23,7 +23,7 @@ from os.path import join
 modname = distname = 'pylint'
-numversion = (1, 5, 1)
+numversion = (1, 5, 2)
 version = '.'.join([str(num) for num in numversion])
 install_requires = [