sql_gen.py: ColDict: Use OrderedDict so that order of keys in input dict (if ordered) will be preserved. This should ensure that tempt table unique indexes have their columns in the same order as the output table, so that a merge join can be used.

util.py: dict_subset(): Use OrderedDict so that order of keys in input dict (if ordered) will be preserved

main Makefile: python-Darwin: Added pip installation instructions. python-Linux: Added ordereddict.

sql.py: DbConn.col_info(): cacheable param defaults to True now that callers explicitly turn off cacheable when needed

sql.py: add_index_col(): Explicitly set update()'s col_info caching depending on whether col_info will be changed later by add_not_null()

sql.py: mk_update(): Renamed cacheable param to cacheable_ so it wouldn't conflict with update()'s cacheable param

sql.py: mk_update(): Added cacheable param to set whether column structure information used to generate the query can be cached

sql.py: add_index_col(): Explicitly set col_info()'s caching depending on whether col_info will be changed later by add_not_null()

sql.py: DbConn.col_info(): Allow caller to specify whether query is cacheable

csv2db: Fixed bug where CREATE TABLE statement was cached, causing it not to be re-executed after a rollback due to a failed COPY FROM. Avoid re-creating the table after a failed COPY FROM, and instead just remove any existing rows.