libg++ updates

[Alexandre Oliva]

Martin's recent enabling of ISO C++ keywords and, or and xor broke
some libg++ classes.  They'd already (mostly) refrain from using those
keywords when compiling in strict ANSI/ISO compliance mode, certainly
because of this issue, but now they fail.  Here's a quick hack that
allows libg++ to keep building.  Manfred, feel free to add them to the
set of standard patches for libg++.