Check GError precondition assertions match standard pattern
Add a checker which warns if a precondition assertion which references a GError**
function parameter doesn’t follow the standard form:
g_return[_val]_if_fail(error == NULL || *error == NULL);
e.g. If the assertion doesn’t check (*error == NULL)
, emit a warning.
(Imported from bugs-everywhere; see #2 (closed).)