sql_gen.py: Added Coalesce class and use it in EnsureNotNull

sql_gen.py: Added coalesce and use it in EnsureNotNull

sql.py: DbConn.col_info(): Don't cache the structure query because the column type, etc. may change between calls. This fixes a bug in mk_update() where the column type would be retrieved before a NOT NULL constraint was added, causing the NOT NULL constraint not to be in the cache info about the column.

sql.py: mk_update(): Implemented in_place mode

sql.py: mk_update(): Factored out filtering of input values so only `.to_str(db)` is used inline in the creation of the query

sql.py: mk_update(): Added in_place param

csvs.py: TsvReader: Prevent "new-line character seen in unquoted field" errors by replacing '\r' with '\n'

csv2db: Adding indexes: Fixed bug where sql.add_index()'s ensure_not_null param needed to be renamed to ensure_not_null_

sql.py: cast(): columns values clause: Use start=0 to avoid "SELECT statement missing a WHERE, LIMIT, or OFFSET clause" warning

inputs/import.stats.xls: Updated for most recent run