Replaced InvalidCollationException (runtime) with proper UnssupportedCollationException
Add try/catch/rethrow for the FDBStoreDataKeyValueIterator to manage a
past_version error that had escaped notice.
Move the exception check into FDBIterationHelper.
Updated UnsupportedCharsetException, so it returns an informative message, also in case an unsupported charset is used
Clean up imports.
merge SytzeH: Throw consistent exceptions for unsupported collations

Merge pull request #1259 from SytzeH/sql-layer/collation
https://github.com/FoundationDB/sql-layer/pull/1259
Merged MID into SUBSTRING, unified testing of SUBSTR, MID and SUBSTRING
merge SytzeH: Merged MID into SUBSTRING, unified testing of SUBSTR, MID and SUBSTRING

Merge pull request #1260 from SytzeH/sql-layer/mid2
https://github.com/FoundationDB/sql-layer/pull/1260
Inject some random delays during MT tests
More care in syncing and marking during MTs
merge tjoneslo: Add try/catch/rethrow for the FDBStoreDataKeyValueIterator

Merge pull request #1258 from tjoneslo/sql-layer/Catch-FDB-exception-and-rethrow
https://github.com/FoundationDB/sql-layer/pull/1258
Alligned behavior from functions: space(), repeat(), lpad, and rpad
merge SytzeH: Alligned behavior from functions: space(), repeat(), lpad(), and rpad()

Merge pull request #1262 from SytzeH/sql-layer/pad
https://github.com/FoundationDB/sql-layer/pull/1262
merge nathanlws: Adjust MT synchronization for deterministic marks

Merge pull request #1261 from nathanlws/sql-layer/mt-tweak-time-checks
https://github.com/FoundationDB/sql-layer/pull/1261
Fix test-space, test-pad as the functions return VARCHAR types, not TEXT
types for the FTS test.
merge tjoneslo: Fix test-space, test-pad

Merge pull request #1265 from tjoneslo/sql-layer/fix-space-tests
https://github.com/FoundationDB/sql-layer/pull/1265