blkfront: write_page needs only to grant read access to the backend

Read operations need to grant write access so the results can
be filled in.

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
blkfront: correct a unit in a comment

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Release 0.2.5

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #7 from djs55/0.2.5

Release 0.2.5