Add gdb.lookup_global_symbol python function.

* NEWS: Add entry.
	* python/py-symbol.c (gdbpy_lookup_global_symbol): New function.
	* python/python-internal.h (gdbpy_lookup_global_symbol): Declare it.
	* python/python.c (GdbMethods): Add entry for lookup_global_symbol.

	doc/
	* gdb.texinfo (Symbols In Python): Document lookup_global_symbol.
	Clarify behaviour of lookup_symbol when `block' argument is omitted,
	add description of result, fix @defun formatting.

	testsuite/
	* gdb.python/py-symbol.exp: Test lookup_global_symbol.

gdb/python/py-symbol.c

@@ -236,6 +236,7 @@ sympy_dealloc (PyObject *obj)
    A tuple with 2 elements is always returned.  The first is the symbol
    object or None, the second is a boolean with the value of
    is_a_field_of_this (see comment in lookup_symbol_in_language).  */
+
 PyObject *
 gdbpy_lookup_symbol (PyObject *self, PyObject *args, PyObject *kw)
 {
@@ -294,6 +295,39 @@ gdbpy_lookup_symbol (PyObject *self, PyObject *args, PyObject *kw)
   return ret_tuple;
 }
 
+/* Implementation of
+   gdb.lookup_global_symbol (name [, domain]) -> symbol or None.  */
+
+PyObject *
+gdbpy_lookup_global_symbol (PyObject *self, PyObject *args, PyObject *kw)
+{
+  int domain = VAR_DOMAIN;
+  const char *name;
+  static char *keywords[] = { "name", "domain", NULL };
+  struct symbol *symbol;
+  PyObject *sym_obj;
+
+  if (! PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &name,
+				     &domain))
+    return NULL;
+
+  symbol = lookup_symbol_global (name, NULL, domain);
+
+  if (symbol)
+    {
+      sym_obj = symbol_to_symbol_object (symbol);
+      if (!sym_obj)
+	return NULL;
+    }
+  else
+    {
+      sym_obj = Py_None;
+      Py_INCREF (Py_None);
+    }
+
+  return sym_obj;
+}
+
 /* This function is called when an objfile is about to be freed.
    Invalidate the symbol as further actions on the symbol would result
    in bad data.  All access to obj->symbol should be gated by