add UBSAN test for clang-3.4 R-dev

Make it easier to do UBSAN test for R packages. [sanitizers](https://github.com/eddelbuettel/sanitizers) is a package to show how this test work.

Here is the [result](https://travis-ci.org/qinwf/sanitizers/builds/43941421) on Travis CI which passed on normal build, but failed on UBSAN build. 
might be worth splitting these into two lines (one for binary installs where we can, one for source installs) just to speed things up.