String.Buffer appears to hang under some circumstances
Imported from http://bugzilla.roxen.com/bugzilla/show_bug.cgi?id=2858
Reported by Martin Nilsson, IDA nilsson@pike.ida.liu.se
It appears that `+= on a String.Buffer object sometimes hangs Pike. Replacing all += operations with the add method solves the problem. I have only encountered this in complex code, so I have no minimized test case. A huge testcase is to rewrite the render_xml method in Parser.XML.Tree to use String.Buffer instead of string concatenation (about 8 lines need to be changed) and build a refdoc manual with the new Parser.XML.Tree.