Automated checkin: version bump for thunderbird 20.0b1 release. DONTBUILD CLOSED TREE a=release

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branch : GECKO200b1_2013030513_RELBRANCH
Added THUNDERBIRD_20_0b1_RELEASE THUNDERBIRD_20_0b1_BUILD1 tag(s) for changeset 3204ef4fb450. DONTBUILD CLOSED TREE a=release

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branch : GECKO200b1_2013030513_RELBRANCH