[dataimport] remove dead code The only caller of ObjectStore._put is ObjectStore.create_entity, which RQLObjectStore overrides (and doesn't call up).

[dataimport] do not use sys.exit() to raise missing argument error Related to #3845572

[dataimport] _create_copyfrom_buffer: add the tests Related to #3845572

[dataimport] _create_copyfrom_buffer: do not ignore columns if data is a list Related to #3845572

[dataimport] _create_copyfrom_buffer: fix datetime converter + add time converter Include second and microsecond in the output instead of dropping them on the floor. The time zone is not supported for now, though. Related to #3845572

[dataimport] _create_copyfrom_buffer: raise ValueError if conversion cannot be performed If the conversion fails, there is no reason to continue execution. One should notify the error. Continuing after a misconverted data could corrupt the database. Related to #3845572

[dataimport] _create_copyfrom_buffer: fix separator check in string converter The empty string is a valid replace_sep. Related to #3845572

[dataimport] _create_copyfrom_buffer: put converters into a list Cleans up the code to avoid a succession of ifs. Related to #3845572

merge 3.19.3 into 3.20 branch

Added tag cubicweb-version-3.19.3, cubicweb-debian-version-3.19.3-1, cubicweb-centos-version-3.19.3-1 for changeset 37f7c60f89f1