Fix for #2500
Fix python test -- Related to #2490
Merge branch 'next' into sam_2156
Revert "Fix for #2500"

This reverts commit 259d473aeef9d330f417269f8492bd3317d1073b.
Removed short-circuit logic for reads in conflict resolving queue altogether
Merge branch 'next' into sam_2156
Merge branch 'daniel_2500' into daniel_concurrent_gc

Conflicts:
	src/arch/io/disk/conflict_resolving.cc
Merge branch 'daniel_concurrent_gc' of github.com:rethinkdb/rethinkdb into daniel_concurrent_gc
Removed pointless tests for whether ctx was NULL or not.
Some whitespace before pointers...
Removed a pointless friend class declaration.
Revert "Removed pointless tests for whether ctx was NULL or not."

This reverts commit ba06bfde7cd7bc7788d9e2e22c5e44f032d37a32.
Removed pointless explanatory comment for destructor decl.
Fixed F'd up indentation of some paramaeters.
Made make_env helper function.
Moved make_env to make_complete_env.
Made stream_cache_t take and hold an rdb_context_t *.
Mode env_t::interruptor const, made the stream cache reconstruct a new env_t.
Made env_t::trace always be empty, so that profiling never happens.  Removed profile_bool_t parameter from its constructors.
Revised a comment.