core: Let Travis build 0.10.x
core: set the  option for Erlang 17.0 and later.
Issue #764

(cherry picked from commit c2d077f2a9937ba1e8afcc4ae9f33d01aaf67a77)
core: recode iso639 module to UTF-8

(cherry picked from commit 3bd42a5dd7f4528043c592e4a485912664fd3bf7)
build: Always use a downloaded rebar

Travis-CI has a rebar version in the shell path which is incompatible
with OTP 17.0.

(cherry picked from commit 43b4ae60a37305bec175cf39c28b2d2e8b7712ea)