Makefile: add EXTRAVERSION support

Add optional EXTRAVERSION parameter to Makefile and allow to mark version
by user friendly label. It might be useful when creating custom
spins of mdadm, or labeling some instance in between major releases.

Signed-off-by: Tkaczyk Mariusz <mariusz.tkaczyk@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>
2 files changed