Put kernel.core_pattern in /etc/sysctl.d/core-dump.conf

This avoids manually patching /etc/sysctl.conf.
Install package "ulimit" on SLES to enable coredumps...

..for both add & remove cases.
Avoid copying pxelinux.0 only if the two files are the same

This allows updating pxelinux.0.
Fix installation of elilo EFI files on SUSE
Make coredump attribute available in the proposal

We already use this attribute, but there was no way to set it from the
proposal.
Merge pull request #166 from vuntz/use-sysctl.d

Put kernel.core_pattern in /etc/sysctl.d/core-dump.conf
Merge pull request #167 from saschpe/release/pebbles/master-sles-coredump-fix

Install package "ulimit" on SLES to enable coredumps
Merge pull request #170 from vuntz/coredump-in-proposal

Make coredump attribute available in the proposal
Merge pull request #169 from vuntz/improve-boot-images

Copy pxelinux.0 if original file changed, and fix installation of EFI files for SUSE