Merge branch 'pa/auto-gc-mac-osx' into maint

Recent Mac OS X updates breaks the logic to detect that the machine
is on the AC power in the sample pre-auto-gc script.

* pa/auto-gc-mac-osx:
  hooks/pre-auto-gc: adjust power checking for newer OS X

contrib/hooks/pre-auto-gc-battery

@@ -33,7 +33,7 @@ elif grep -q "AC Power \+: 1" /proc/pmu/info 2>/dev/null
 then
 	exit 0
 elif test -x /usr/bin/pmset && /usr/bin/pmset -g batt |
-	grep -q "Currently drawing from 'AC Power'"
+	grep -q "drawing from 'AC Power'"
 then
 	exit 0
 fi