Update version to reflect this branch is for post-1.1.x development.

Update version to reflect this branch is for post-1.1.x development.

When development for a new long-term release is started, we haven't
typically updated the version string.  This means that version numbers
used in binaries generated on this branch tend to lag behind "current"
stable releases.  We considered using a "pre" string in the version
(eg, "1.2.0-pre1") but this causes some pain for RPMs.  Instead, we
will now use "90" as the version's bug-fix number to indicate that this
will form a new release.

For example, the current stable series is "1.1.x" in the "branch-1.1"
branch, so the master branch will be labeled "1.1.90" in anticipation
that it will be the basis for the "1.2.x" series.  Code in "branch-1.1"
will have the expected version numbers (ie, 1.1.0, 1.1.1, 1.1.2, etc)
and versions in-branch will lag slightly before an official release.

Suggested-by: Ben Pfaff <blp@nicira.com>