Fold all consecutive whitespaces into single blanks. This avoids problems

Fold all consecutive whitespaces into single blanks. This avoids problems
when minor whitespace changes occur in the original templates; it also
makes the strings much easier to read (e.g., instead of "foo\n\n\t\t  bar",
xgettext.pl will now always generate "foo bar" and tmpl_process3.pl will
understand it to be the same as the original string).