collectd: Update to 5.4.1

-update collectd to the current release 5.4.1
-fix sigrok glib check (upstream patch after 5.4.1)

Note:
Changes are required also to luci-statistics in Luci source.
Patch in http://patchwork.openwrt.org/patch/5303/

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>
Merge pull request #298 from hnyman/collectd541

collectd: Update to 5.4.1
openvswitch: move openvswitch-common/postinst after install
openvswitch: merge openvswitch-common + openvswitch-switch into openvswitch
openvswitch: organize openvswitch-ipsec and openvswitch-benchmark as subpackages
openvswitch: change order of the installs
openvswitch: fix package URL
openvswitch: remove openvswitch-package until python package is put back in
openvswitch: add openvswitch-python subpackage

Requires python package.
Required by other openvswitch subpackages (like openvswitch-python).
openvswitch: add openvswitch-ipsesc package back