Require Python 3.4

I believe we previously agreed that the minimum supported Python
version should be 3.4.  This patch makes this change, harmonizing the
documentation (which was inconsistent about the minimum version) and
the code.

New in v2: rebased, and removed a pre-3.4 workaround from __init__.py.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Approved-by: Kevin Buettner <kevinb@redhat.com>
Acked-By: Tom de Vries <tdevries@suse.de>
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31870

gdb/python/python-internal.h

@@ -88,6 +88,8 @@
 #include <frameobject.h>
 #include "py-ref.h"
 
+static_assert (PY_VERSION_HEX >= 0x03040000);
+
 #define Py_TPFLAGS_CHECKTYPES 0
 
 /* If Python.h does not define WITH_THREAD, then the various
@@ -135,17 +137,6 @@ typedef unsigned long gdb_py_ulongest;
 
 #endif /* HAVE_LONG_LONG */
 
-#if PY_VERSION_HEX < 0x03020000
-typedef long Py_hash_t;
-#endif
-
-/* PyMem_RawMalloc appeared in Python 3.4.  For earlier versions, we can just
-   fall back to PyMem_Malloc.  */
-
-#if PY_VERSION_HEX < 0x03040000
-#define PyMem_RawMalloc PyMem_Malloc
-#endif
-
 /* A template variable holding the format character (as for
    Py_BuildValue) for a given type.  */
 template<typename T>