Porting pretty printers to Python 2+3

[Samuel Bronson]

I have two patches:

[PATCH 1/2] Make libstdc++ testsuite work with pre-color GCC versions

This is just to make it easy to test my changes, since my computer is
evidently too pathetic to build GCC.

[PATCH 2/2] Port libstdc++ pretty-printers & assiocated tests to Python2+3

My goal here is to do what Mathias Klose originally tried to do with
<http://patchwork.ozlabs.org/patch/287368/>; my patch is somewhat
loosely based on his.

(I guess I'm going to need to work in a reference to
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58962> ...)

My changes give me the exact same set of failures in GDB 7.7 when
linked with python2.7 and with python3.3, for what seem to be the
exact same reasons; I'm expecting them to go away in GDB 7.7.1 once I
get that built.

Besides review, I believe I also need an Assignment Form -- I'm
assuming I can't get away with claiming that this code is effectively
part of GDB, and that my GDB assignment papers are thus all I need?

To actually run the tests, I configured just the libstdc++-v3 subtree
and then ran:

$ make check RUNTESTFLAGS='--debug --directory libstdc++-prettyprinters'

over and over again in my build tree.  The GDBs used were WIPs from
the Debian packaging, if that matters.

If there's anything unclear about what I've done here, speak up so I
can clarify the comments on the conditionalized code.