Include traceback with failures (even without fail-fast).

Testing Done:
Ran tests.

Reviewed at https://rbcommons.com/s/twitter/r/1226/
Fix a bug where all OptionValue objects had the same underlying forwardings.

This wasn't seen earlier because in practice all tasks migrated so far had
disjoint option names.

This was exposed when I migrated two unrelated tasks that happened to have
an identically named option (--skip).

Testing Done:
CI passed.

Verified that this fixes the name collision issue that triggered its discovery in the first place.

Reviewed at https://rbcommons.com/s/twitter/r/1229/
move ide_gen.py and friends idea_gen.py and eclipse_gen.py to new options

Move ide_gen.py and friends idea_gen.py and eclipse_gen.py to new options

Testing Done:
CI is running.

Bugs closed: 736

Reviewed at https://rbcommons.com/s/twitter/r/1230/
change thrift_linter.py to use new register_options

Testing Done:
Take two. Previous change accidentally added "default=False" which was inappropriate and ended up breaking the logic that falls back to a value defined in the BUILD file. Now we explicitly default the flag to None and preserve the desired logic.

I ran the integration tests related to thrift linter, which I inadvertently broke in my last attempt at this:
  devpants goal test tests/python/pants_test/tasks:thrift_linter_integration

Reviewed at https://rbcommons.com/s/twitter/r/1225/
Fix spacing in thrift_linter.py
Allow UTF-8 characters in changelog

Testing Done:
Tests pass, except that sometimes they fail on travis because
sys.stdout.encoding.

Reviewed at https://rbcommons.com/s/twitter/r/1228/
Minimal target "tags" support

This doesn't provide any addtional end-user functionality, but has been useful as a channel for custom tasks and BUILD files to communicate addtional information about targets.

We've been rebasing this change on top of upstream pants for releases at Foursquare for a few months now and we've found it useful in implmenting downstream custom tasks (like our graph rules), which need a place to put additional information in the build graph, while staying out of the internally meaningful things like `labels`.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/39211424

Reviewed at https://rbcommons.com/s/twitter/r/1227/