Merge pull request #2429 from andyli/travis

TravisCI: all targets enabled!
Metadata should be MetadataEntry as in ocaml source

Definition in Ocaml: 

TMeta of metadata_entry * texpr
Merge pull request #2430 from frabbit/patch-4

Metadata should be MetadataEntry as in ocaml source
TravisCI: run apt-get update before installing ia32-libs
"libgd2-xpm", "ia32-libs", "ia32-libs-multiarch" have to be installed at the same time. And they combined is a huge amount of libs… Try to run “apt-get update” and use “travis_retry” to reduce the chance of having network error.
“flashplugin-installer" is not used but forgot to remove.