bump to 0.6.3

bump to 0.6.3

he most important updates of this release are:
 - fix memory leak in sockfd cache
 - fix latent segfault in event loop

If no one complains about this release in 2 days, it will be v0.6.3
officialy.

Below is the summary of commits this release contains.

Hitoshi Mitake (2):
      collie: remove a compiler warning
      sheep: correct a way of freeing sockfd_cache_entry

Kai Zhang (1):
      sheep: fixed compile warning

MORITA Kazutaka (2):
      sheep: make invalid_vnode() type safe
      event: refresh event info after unregistering

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>