Implemented cross-coroutine backtraces.
Minor improvements
adding check for NULL character in r.js return value before constructing datum_t
Javascript driver: do not install the C++ protobuf lib by default

Review 1027 by @neumino
Closes #1172
Remove DEPENDENCIES file

Review 1026 by @neumino
Closes #697
Merge branch 'daniel_cross_coro_backtraces' into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
Remove anaphoric macros

Review 1005 by @mlucy
Closes #806
Bump fetched gperftools to 2.1

Review 1029 by @tryneus
Closes #1549
Merge branch 'next' into sam_97_alt