Merge branch 'ab/pre-auto-gc-battery'

A sample auto-gc hook (in contrib/) to skip auto-gc while on
battery has been updated to almost always allow running auto-gc
unless on_ac_power command is absolutely sure that we are on
battery power (earlier, it skipped unless the command is sure that
we are on ac power).

* ab/pre-auto-gc-battery:
  hooks/pre-auto-gc-battery: allow gc to run on non-laptops

contrib/hooks/pre-auto-gc-battery

@@ -17,7 +17,7 @@
 # ln -sf /usr/share/git-core/contrib/hooks/pre-auto-gc-battery \
 #	hooks/pre-auto-gc
 
-if test -x /sbin/on_ac_power && /sbin/on_ac_power
+if test -x /sbin/on_ac_power && (/sbin/on_ac_power;test $? -ne 1)
 then
 	exit 0
 elif test "$(cat /sys/class/power_supply/AC/online 2>/dev/null)" = 1