variable: Do not trim trailing whitespace from variable labels.

variable: Do not trim trailing whitespace from variable labels.

Until now, PSPP has trimmed trailing whitespace from variable
labels.  SPSS does not do this, which led to gratuitous changes
in variable labels when reading and then writing back a .sav
file, so this commit stops stripping trailing whitespace from
variable labels.

Thanks to Curt Reinhold <Curt.Reinhold@psychonomics.de> for
providing the .sav file that led to this discovery.