ccpp: save abrt core files only to new files

Prior this commit abrt-hook-ccpp saved a core file generated by a
process running a program whose name starts with "abrt" in
DUMP_LOCATION/$(basename program)-coredump. If the file was a symlink,
the hook followed and wrote core file to the symlink's target.

Addresses CVE-2015-5287

Signed-off-by: Jakub Filak <jfilak@redhat.com>