Fix incorrect stacklevel for DeprecationWarnings originating from the struct module.
Also clean up related tests in test_struct.
The stacklevel fix should be backported to 2.6 once that branch is unfrozen.
diff --git a/Modules/_struct.c b/Modules/_struct.c
index 27f8881..d7cc77f 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -121,7 +121,7 @@
 	}
 #ifdef PY_STRUCT_FLOAT_COERCE
 	if (PyFloat_Check(v)) {
-		if (PyErr_WarnEx(PyExc_DeprecationWarning, FLOAT_COERCE, 2)<0)
+		if (PyErr_WarnEx(PyExc_DeprecationWarning, FLOAT_COERCE, 1)<0)
 			return NULL;
 		return PyNumber_Long(v);
 	}