Support suppressed property when deserializing Throwable

[klaasdellschaft]

Closes #3177

When this solution for #3177 is OK, I would suggest to continue refactoring ThrowableDeserializer.deserializeFromObject(...) such that code duplications are removed / the method gets shorter. For example, the following snippet exists twice in the method

// any pending values?
if (pending != null) {
    for (int i = 0, len = pendingIx; i < len; i += 2) {
        prop = (SettableBeanProperty)pending[i];
        prop.set(throwable, pending[i+1]);
    }
    pending = null;
}

[cowtowncoder]

Sounds good. I will be out of town over the weekend, but will get back to this next week.

One thing I'd need (unless it's already done) to eventually merge the PR is CLA:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

which only needs to be sent once and is good for all Jackson contributions.
It's usually done by printing, filling & signing, scanning/photo, email to info at fasterxml dot com.
(digital version is fine too, wrt modified pdf).
No hurry, only needed after review, but I'll mention it now.

[cowtowncoder]

Instead of calling via JsonParser, should go through DeserializationContext; this will keep current context and settings (JsonParser route will create new context with possibly differing settings -- at least until Jackson 3.0)

[klaasdellschaft]

OK, changed the corresponding line to

suppressed = ctxt.readValue(p, Throwable[].class);

[cowtowncoder]

@klaasdellschaft Aside from one minor comment, looks good (assuming it works). Are changes needed?
If not, I'd just need the CLA and would be happy to merge this and see about refactoring you suggested.

[klaasdellschaft]

CLA is sent, and a small refactoring is applied such that duplicated code blocks are removed. From my point of view, ready for merging.