support for empty passwords

[ixcat]

in my test environment, my user is configured without a password. this triggers the following errors:

• dj.conn doesn't treat explicit-blank password as a valid value, which triggers prompting
• gui version of password prompt will return an empty array rather than a blank string (console prompt function appears to accept/return the desired0x0 empty char array (what '' returns at a prompt), tested this route from direct call rather than via dj.conn() )
• (needs more direct testing to confirm this point) lower-level connection function doesn't seem to accept blank as a valid value and fails:

Error using mym
All args must be strings, except id