Log Message:
Updated abcm2ps to 8.13.11.

---- Version 8.13.11 - 2017-06-15 ----

Fix crash when twice a same voice in %%score inside tune
Fix some compilation warnings and crash with gcc-5.4
	(reported by Guido Gonzato and more people)
Fix more crashes in recent versions of MacOS X
	(reported by David Lacroix)