fix smart attribute comparison

Each S.M.A.R.T. attribute is compared against a threshold. If it is LESSTHAN
that threshold an error is reported.  This patch fixes the problem, that
attribute values EQUAL to the threshold are reported as error, which is wrong.
Only LESSTHAN the threshold is an error.

For more information see: http://www.hdsentinel.com/smart/index.php

My SSD has some attributes which value and threshold are "0". Without the patch
this is reported as errornous.

ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE
...
172 Unknown_Attribute 0x0032 000 000 000 Old_age Always - 0
174 Unknown_Attribute 0x0030 000 000 000 Old_age Offline - 13
177 Wear_Leveling_Count 0x0000 000 000 000 Old_age Offline - 0
...

See also:

* http://sourceforge.net/p/nagiosplug/patches/365/
* https://bugzilla.redhat.com/913085