This bumps the copyright years to the appropriate years after not
having been updated for some time.  Also reformats existing code
headers to match the upstream style to ensure consistency.

It's pretty much identical to Form_pg_appendonly, which is now available
in the relcache. No need to pass this additional struct around.

This way, you don't need to always fetch it from the system catalogs,
which makes things simpler, and is marginally faster too.

To make all the fields in pg_appendonly accessible by direct access to
the Form_pg_appendonly struct, change 'compresstype' field from text to
name. "No compression" is now represented by an empty string, rather than
NULL. I hope there are no applications out there that will get confused
by this.

The GetAppendOnlyEntry() function used to take a Snapshot as argument,
but that seems unnecessary. The data in pg_appendonly doesn't change for
a table after it's been created. Except when it's ALTERed, or rewritten
by TRUNCATE or CLUSTER, but those operations invalidate the relcache, and
we're never interested in the old version.

There's not much need for the AppendOnlyEntry struct and the
GetAppendOnlyEntry() function anymore; you can just as easily just access
the Form_pg_appendonly struct directly. I'll remove that as a separate
commit, though, to keep this one more readable.

Many headers in src/include/catalog have gotten this treatment in the
upstream. This makes life easier for the next commit, which adds a
reference to Form_pg_appendonly to RelationData. With this separation,
we can avoid pulling in a lot of other headers into rel.h, and avoid a
circular dependency,