Stop writing out '== NULL' and '!= NULL'
Currently glib-networking code style is inconsistent on whether to test for NULL using !pointer or pointer == NULL. This is harmful because it forces us to think and make a decision each time when writing such conditions.
We have somewhat-arbitrarily agreed to stop writing this out longways. The tiebreaker is the C++ core guidelines (endorsed by the C++ standardization people):
glib-networking is not C++, but the decision either way is arbitrary, so this seems like as good a tiebreaker as any. Also, WebKit requires it this way, and therefore so does Epiphany.
Fixes #72 (closed)