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ARROW-334: [Python] Remove INSTALL_RPATH_USE_LINK_PATH

Will try to verify whether this resolves the issue. See https://travis-ci.org/conda-forge/staged-recipes/builds/166897102

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #171 from wesm/ARROW-334 and squashes the following commits:

ed8fa39 [Wes McKinney] Switch by to xcode 6.4
b8224ce [Wes McKinney] Escape dollar sign in ORIGIN
b76b7ac [Wes McKinney] Fix LD_LIBRARY_PATH
3c8d2dd [Wes McKinney] Clean up Travis CI scripts a bit. Put  in LD_LIBRARY_PATH
30488d7 [Wes McKinney] Don't conda install arrow-cpp during Travis build
afb1dc0 [Wes McKinney] Remove INSTALL_RPATH_USE_LINK_PATH