print_wrapped_text(): allow hard newlines

print_wrapped_text(): allow hard newlines

print_wrapped_text() will insert its own newlines. Up until now, if the
text passed to it contained newlines, they would not be handled properly
(the wrapping got confused after that).

The strategy is to replace a single new-line with a space, but keep double
new-lines so that already-wrapped text with empty lines between paragraphs
will be handled properly.

However, single new-line characters are only handled this way if the
character after it is an alphanumeric character, as per Linus' suggestion.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>