Improve build instructions

Make it clear that when building directly from the Git tree
the configure script must be manually generated by running the
autogen.sh script.  This requires that the GNU autotools packages
be installed for your distribution.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes zfsonlinux/zfs#1448
Merge branch 'upstream' into snapshot/ubuntu/saucy
Use dh_autoreconf.

Let debhelper call autoreconf automatically instead of invoking
autogen.sh in the configure rule.
Use dh_auto_configure.

Let debhelper call the ./configure script with automatic options.
Revert "Set extend-diff-ignore='.*' in the debian/source/options file"

This reverts commit 69014268658302f1239d3580c4a80e4371edf766.

Each release series is now built from a separate branch.
Update changelog for 0.6.1-2~saucy~2.gbpd297e0 release