disallowed referencing variables from inside secondary index functions (c.f. Issue #718)
added comment and changed to private inheritance for special_var_shadower_t
Bump serializer version to 1.5

Closes #774

Review 518 by @srh
merge
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
improved batching and added verbose option to import_export.rb (c.f. Issue #782)
fixed typo
Merge branch 'next' into sam_etc_deheaderize