revlog: reduce memory usage in addgroup - use a buffer to extract the delta from a chunk - avoid concatenating to a compressed delta - use a buffer to directly extra full text from a trivial delta - delete chunk and delta objects after use

changeset:   0:61c9426e69fe
tag:         tip
user:        test
date:        Thu Jan 01 00:00:00 1970 +0000
summary:     test

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200 Script output follows
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[('content-type', 'text/html; charset=ascii')]
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