Minor fix in IceModelVec2S::put_on_proc0().
Add a compile-time option to support clang on OS X 10.9.

Set Pism_USE_TR1 to "ON" if your compiler provides C++ shared pointers
in the std::tr1 namespace and you use "#include <tr1/memory>".

Set Pism_USE_TR1 to "OFF" if you compiler *does not* provide shared
pointers in the std::tr1 namespace (i.e. they are in std) and you
use "#include <memory>".

"ON" is the default, to support older compilers and because some newer
compilers support both "#include <memory>" and "#include <tr1/memory>".