scripts/sequence-patch.sh: Skip Xen patches when Xen configs are disabled.

When updating the base kernel version, the Xen patches must be updated
separately. This allows us to skip the Xen patches until they're resynced
just by disabling the configs.
scripts/tar-up.sh: Disable Xen patches when Xen configs are disabled

Similar to the change for scripts/sequence-patch.sh, this change
disables the Xen patches with +noxen in series.conf when creating
the kernel-source package.
scripts/sequence-patch.sh: Fix for Xen detection with --vanilla

When we hit the limit code to handle $SKIP_XEN and there aren't
any Xen patches to apply anyway, we'll fail because LIMIT is unset.
scripts/rpm-changes-merge.pl: Stop warning about duplicate keys

There is nothing wrong about two changelong entries having same date to
warrant such a warning.
README: update URL of abbreviation list

The page with current set of abbreviations for References tag
has been moved, update the URL.
scripts/tar-up.sh: Fix typo: ec3 -> ec2
scripts/sequence-patch.sh: Do not exit prematurely when skipping patches
scripts/sequence-patch.sh: Use a default value for --config

Copy the default config for the current architecture (on ix86, this
means pae). Also, fix a typo in the message printed.
scripts/run_oldconfig.sh: Add AArch64 support
scripts/sequence-patch.sh: Add a .is_vanilla marker to vanilla trees
scripts/run_oldconfig.sh: Default to --vanilla in vanilla trees
Delete scripts/unpack-kernel.sh.

This script stopped working with kernel 3.0 and nobody complained,
which suggests nobody has actually used it for over 2 years. So let's
just delete it.
sequence-patch: Add support for xz-compressed archives
sequence-patch: Drop support for compressed patches

As suggested by Michal Marek. We never had them in the tree.
sequence-patch: Drop set but unused local variable in restore_files
sequence-patch: Omit patch backup options in dry-run mode

Patch options --backup, --prefix and --no-backup-if-mismatch have no
effect when running with --dry-run.
sequence-patch: Clean up when patch fails to apply

If a patch fails to apply, we shouldn't keep its backup files in .pc/.
They are no longer needed and may confuse quilt.

Also, if a patch is skipped because it can be applied reversed, the
resulting tree should be as if the patch wasn't in the series at all.
This means we shouldn't leave .rej files behind, nor the backup .pc/
directory for that patch.
sequence-patch: No comments in .pc/applied-patches

Quilt does not handle comments in .pc/applied-patches, so do not
list patches which could be applied reversed as comments in that
file. Doing so causes "quilt applied" for example to return bogus
results.
sequence-patch: Clean up in the foreground

Benchmarking shows that the benefits of background clean-up when
running on tmpfs are marginal, while the penalty when running on a
spinning hard-disk drive is significant. So just clean up in the
foreground in all cases.
scripts/sequence-patch.sh: Use the vanilla config on vanilla-only branches