Use SPACE as delimiter when joining multiple lines.

Currently, when users use ctrl+mouse to select and copy multiple lines,
those lines are joined into single line in a seamless way. LINEBREAK is
simply removed, thus the first character of second line will be
positioned right after the last character of the first line. This patch
replaces the LINEBREAK with a SPACE.

Thanks to Jekyll Wu () for patch and research.

FIXED-IN: 4.8