Added utf-8 headers to all python files

Added # content=utf-8 headers to all python files

If you use any non-ascii unicode in a file, this is required.

See a follow on patch  https://rbcommons.com/s/twitter/r/524/ that adds a test so we will check to see that new files contain the header.

This is a mechanical change, I used this script:

#!/bin/bash

for i in $(cat /tmp/files.out) ; do
  FILE=$i
  HEAD=$(head -1 ${FILE})
  if [ -f "${FILE}" -a "# coding=utf-8" != "${HEAD}" ] ; then
    mv "${FILE}" "${FILE}.tmp"
    if [ $? != 0 ] ; then
      echo "Couldn't move '${FILE}'"
      exit 1
    fi
    echo '# coding=utf-8' > ${FILE}
    cat ${FILE}.tmp >> ${FILE}
    rm ${FILE}.tmp
  else
    echo "********* HEAD was ${HEAD}"
  fi
done

Testing Done:
running ci.sh

See https://rbcommons.com/s/twitter/r/524/

Bugs closed: 227

Reviewed at https://rbcommons.com/s/twitter/r/523/
Kill the now unused Group class.

Testing Done:
$ ./build-support/bin/ci.sh

Bugs closed: 229

Reviewed at https://rbcommons.com/s/twitter/r/527/
Added a test to show that all files have 'coding=utf8' on them

This is a followon to https://rbcommons.com/s/twitter/r/523

which adds a test to show that all python files under the repo have '# coding=utf8' as the first line

Testing Done:
ci.sh passed

Bugs closed: 227

Reviewed at https://rbcommons.com/s/twitter/r/524/
    (Accidentally omitted last change from review)

    Added a test to show that all files have 'coding=utf8' on them

    This is a followon to https://rbcommons.com/s/twitter/r/523

    which adds a test to show that all python files under the repo have '# coding=utf8' as the first line

    Testing Done:
    ci.sh passed

    Bugs closed: 227

    Reviewed at https://rbcommons.com/s/twitter/r/524/
Fixup Utf8HeaderTest - use original python target sources only.

Restrict the Utf8HeaderTest to python files checked in on disk
by converting from an fs walk to a build file walk.

Button up the build file walk machinery in the build file parser
and convert existing usages to this new api.

Fixup BUILD dependencies.

Testing Done:
Currently red on travis-ci: https://travis-ci.org/pantsbuild/pants/jobs/27673541 :
...
E       AssertionError: Expected these files to contain first line "# coding=utf8": ['/home/travis/build/pantsbuild/pants/.pants.d/gen/thrift/combined/gen-py/__init__.py',

Now passes:
$ ./build-support/bin/ci.sh

Also ran refactored task tests individually to help confirm BUILD deps:
$ PANTS_DEV=1 ./pants goal test tests/python/pants_test/tasks/:listtargets
$ PANTS_DEV=1 ./pants goal test tests/python/pants_test/tasks/:filemap
$ PANTS_DEV=1 ./pants goal test tests/python/pants_test/tasks/:check_published_deps
$ PANTS_DEV=1 ./pants goal test tests/python/pants_test:test_utf8_header

Bugs closed: 236

Reviewed at https://rbcommons.com/s/twitter/r/537/
Merge branch 'master' of github.com:pantsbuild/pants into areitz/pants/fix_wiki
Address John and Larry's feedback