0_6_0_24 Sync to core team's development branch

Rework after code review
Statistics refactoring

Also applied the following patches:
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From: Hiroshi Shimamoto <h-shimamoto at ct.jp.nec.com>

[PATCH development] datapath/dpdk: regression missing to call,
ovs_flow_used_time()
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From: Shu Shen <GitHub username: shushen>

Clean up git repository, adding .gitignore and remove auto-generated
files, chmod for boot.sh
Fix compile error when SSE4.2 is not enable for build
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