Add single file-type filter#5

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i3zhe wants to merge 6 commits intoprotocool:masterfrom

Commits on Mar 6, 2012

add extentsion filter
Jerry Huo
committed

Commits on Mar 7, 2012

add comments. remove debug traces
Jerry Huo
committed
new branch
Jerry Huo
committed
Fix multi filter bug
Jerry Huo
committed

Commits on Mar 8, 2012

support only small filters
Jerry Huo
committed
strip spaces of filter
Jerry Huo
committed