updated term_walker and changed to a switch statement to catch future omissions (c.f. Issue 749)
expanded switch statements
fix a lazy crashing bug (c.f. Issue #757)
Merge branch '749_update_term_walker' into next
fixed merge bug
Merge branch 'next' into sam_libcxx
Merge branch 'sam_libcxx' into sam_libcxx_DiskConflictTest
Merge branch 'next' into sam_no_ptr_bag

Conflicts:
	src/rdb_protocol/env.cc