D 2.0 support in SVN

[David Friedman]

GDC now has support for D 2.0!  I have tested it on Linux and Darwin so far.

So as to not break other projects, the svn code still builds D 1.0 by 
default.  To build 2.0, run setup-gcc.sh like this:

gcc/d/setup-gcc.sh --d-language-version=2

When GDC 0.25 is released, I will probably make 2.0 the default.  Source 
packages will contain only either 1.0 or 2.0 and will not need a special 
option.

David