Created attachment 174327 [details]
Allow ::= and add a man-page entry.
The `::=' operator have previously been accepted into the next issue of
the 'Open Group' standards (http://austingroupbugs.net/view.php?id=330).
The `::=' assignment operator is equivalent to the `:=' assignment
operator in bmake, so the patch adds `::=' by allowing an additional
colon preceding `:='.
Simon might already be aware of this.