Fix relativity of antlr sources

This fixes an issue where CacheValidator's source hashing was failing on
the synthetic targets generated by AntlrGen, since the assumed source
paths mismatched the actual generated paths.

- Adds an integration test for antlr4 codegen
- Uses sources_relative_to_source_root for the assumed output sources,
  and fixes the synthetic source root for the antlr output. We can't
  control antlr's output relative paths very tightly, so we can't use
  the output directory directly as a sourceroot.
Lock globs into rootdir and below

This avoids the situation where a user adds a sources=globs('../*.scala'), causing it to be silently ignored but causes issues later.

Reviewed here: https://rbcommons.com/s/twitter/r/686/
Closes: https://github.com/pantsbuild/pants/issues/348
Pluralize product_type of Task to product_types
doc: Python doc, don't use twitter/commons as example

Back when Pants' source code lived in twitter/commons, it made sense to use example code from there. Nowadays, not so much. Use Pants' own src/python/example instead.

Instead of having sample code in the doc, "include" from src/python/example; that's easier to keep correct.

Testing Done:
build-support/bin/publish_docs.sh

Reviewed at https://rbcommons.com/s/twitter/r/654/
Stop pointing twitter/commons users at the "old python" docs

Reviewed at https://rbcommons.com/s/twitter/r/693/
make build_configuration test happy on OSX, not just linux

"Looks like we need to toss in a realpath somewhere in these tests" was true

Also a couple of missing deps reared their head when I ran this test on its own

Testing Done:
./pants goal test tests/python/pants_test/base:build_configuration

./build-support/bin/ci.sh # on my mac

Linux still happy
https://travis-ci.org/pantsbuild/pants/builds/30092011

Reviewed at https://rbcommons.com/s/twitter/r/694/
Updated junit-runner to 0.0.41 to be able to use guava version > 15
exclude guava from junit-runner in BUILD.tools explicitly to show where you
  need to update the guava version in case you want to use 17 or higher
Bumped guava version in 3rdParty, added TODO and docs on what is going on with guava in BUILD.tools