Stop using BuildStepStatus when running steps
Update status string handling for most tests

There are still some failing tests due to a lingering issue around
BuildStep no longer supporting a `describe` method.
add more compatibility for old-style steps

* BuildStep implements describe()
* Factor out command_to_string
Fix ShellSequence status strings; do error reporting in twistd.log
fix remaining tests
Remove the BuildSetStatus class, still allowing unpickling
remove LogFile and HTMLLogFile to buildbot.util.pickle
add tests for get{Current,Result}Summary
Merge branch 'bug2818' of github.com:djmitche/buildbot into pr1238
fix trivial 2.6 incompatibility

https://docs.python.org/2/library/stdtypes.html?highlight=decode#str.decode

Changed in version 2.7: Support for keyword arguments added.

Signed-off-by: Pierre Tardy <pierre.tardy@intel.com>