base

Fix documentation for Parcel.readException().

The old documentation was kind of useless and not clear, so this is an
improvement.

In addition to this change, I think this method should probably be private
instead of public, especially since the values for code are private. But it's
too late to change that now. Also the method name is pretty poor, since it's
not actually reading anything. Something like "throwException" would be more
appropriate.

I'm open to suggestions on how to improve this situation. Maybe mark the
method as deprecated with a comment that it will be made private in the
future?

Change-Id: I830f2bcf606714bd130d8c953aa33974b33c9a83