Werk #3168: Fix duplicate loading of check that have a copy in local/share/check_mk/checks.

Component	Core & setup
Title	Fix duplicate loading of check that have a copy in local/share/check_mk/checks.
Date	Feb 7, 2016
Level	Trivial Change
Class	Bug Fix
Compatibility	Compatible - no manual interaction needed
Checkmk versions & editions	1.2.7i4 Checkmk Community, Checkmk Pro, Checkmk Ultimate MT

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