clang/gcc: Fix compilation issues with clang 3.0 and gcc 4.6

clang/gcc: Fix compilation issues with clang 3.0 and gcc 4.6

This patch addresses a number of minor issues that cause problems when
compiling with clang >= 3.0 and gcc >= 4.6. Most importantly, it
avoids using the deprecated ext/hash_map and instead uses
unordered_map (and similarly so for the hash_set). To make use of the
new STL containers, g++ and clang has to be invoked with "-std=c++0x",
and this is now added for all gcc versions >= 4.6, and for clang >=
3.0. For gcc >= 4.3 and <= 4.5 and clang <= 3.0 we use the tr1
unordered_map to avoid the deprecation warning.

The addition of c++0x in turn causes a few problems, as the
compiler is more stringent and adds a number of new warnings. Below,
the most important issues are enumerated:

1) the use of namespaces is more strict, e.g. for isnan, and all
   headers opening the entire namespace std are now fixed.

2) another other issue caused by the more stringent compiler is the
   narrowing of the embedded python, which used to be a char array,
   and is now unsigned char since there were values larger than 128.

3) a particularly odd issue that arose with the new c++0x behaviour is
   found in range.hh, where the operator< causes gcc to complain about
   the template type parsing (the "<" is interpreted as the beginning
   of a template argument), and the problem seems to be related to the
   begin/end members introduced for the range-type iteration, which is
   a new feature in c++11.

As a minor update, this patch also fixes the build flags for the clang
debug target that used to be shared with gcc and incorrectly use
"-ggdb".