Slight tweaks to README
Slight tweaks to README

* change "autoscan" dependency to "autoconf" since that's the name
  of the package
* add python as a dependency (Binglin ran into this issue on his
  stripped-down Ubuntu image)
* Delineate the section on dealing with gcc 4.4 so people can skip
  reading it if they have a modern compiler.

Change-Id: I3616f63b63c5de4fa387fbb431a5a73db581326a
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5120
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: jenkins

andrwng/kudu,cloudera/kudu,cloudera/kudu,cloudera/kudu,andrwng/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu,EvilMcJerkface/kudu,andrwng/kudu,InspurUSA/kudu,andrwng/kudu,EvilMcJerkface/kudu,helifu/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,andrwng/kudu,helifu/kudu,helifu/kudu,cloudera/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,andrwng/kudu,andrwng/kudu,helifu/kudu,EvilMcJerkface/kudu