Change some aspects of the PRINT, PRINT EJECT, and WRITE

transformations to more closely match SPSS behavior:

- PRINT puts spaces between variables, unless a format is specified
explicitly.

- WRITE doesn't put space between variables.

- PRINT to an external file prefixes each line with a space.

- PRINT EJECT to an external file indicates a formfeed by a "1" in the
first column.

- WRITE writes out spaces for system-missing values, not a period.

- When no output is specified, an empty record is output.

Also, update documentation and tests to match this behavior.