Strange payloads in notifications

[kzangeli]

We have detected a few pretty strange notification payloads, for example in:
test/functionalTest/cases/0876_attribute_dates/attrs_dates_overridden_by_user_subs.test
... where identical payloads in notifications have different Content-Length.
The entire difference is probably whitespace, but we need to look into this.

[fgalan]

The change we need to do in that file was:

-Content-Length: 262
+Content-Length: REGEX((400|262))

[fgalan]

Additionally in test/functionalTest/cases/1048_subscription_cache/three_subscriptions.test we need to change:

-Content-Length: 22REGEX(\d)
+Content-Length: REGEX(\d+)

although the one we intially used, 22REGEX(\d), was also pretty weird...

[fgalan]

The PR from which the modifications come from, for reference: apinf#34

[kzangeli]

One more of these strange content-Lengths of payloads:
0876_entity_dates/entity_dates_overridden_by_user_subs.test, PR apinf#35