Add build/ dir for alterl bindings and remove them from .gitignore

Summary: These files are copied from the erl/build dir. I don't know why
         I accidentally gitignored them before.


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@666413 13f79535-47bb-0310-9956-ffa450edef68
8 files changed