Honor CASCADE in TRUNCATE TABLE.
Updated README including big warning
Make row reader retry more careful in case of commit failure on final try.
merge oriherrnstadt: Updated README including warning

Merge pull request #890 from oriherrnstadt/sql-layer/update-readme
https://github.com/FoundationDB/sql-layer/pull/890
merge MMcM: Support truncate group

Merge pull request #887 from MMcM/akiban-server/truncate-group
https://github.com/FoundationDB/sql-layer/pull/887
merge MMcM: Make row reader retry more careful in case of commit failure on final try

Merge pull request #891 from MMcM/akiban-server/row-reader-retry-2
https://github.com/FoundationDB/sql-layer/pull/891