Update Makefile

Review of https://bugzilla.redhat.com/show_bug.cgi?id=1015765:

1. I don't think we need to define DESTDIR?=/ in makefile, this is an optional option for many distros.

2. Preserve the timestamp of install with -p option.

3. We should define PREFIX, as some distros may use /usr/local.
Merge pull request #1 from cicku/patch-1

Update Makefile