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.

sql.py: add_index(): Don't generate a unique name for the index because the database does that automatically