Support CMake 2.8

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Currently we use get_filename_component( .. DIRECTORY ) which is a CMake>2.8 feature. Replacing it with PATH will add support for older CMake versions.

Note: That is enough to build Apache Arrow C++ on Debian Wheezy.

Reporter: Uwe Korn / @xhochy
Assignee: Uwe Korn / @xhochy

_{Note: This issue was originally created as ARROW-73. Please see the migration documentation for further details.}

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Uwe Korn / @xhochy:
PR: #31

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Wes McKinney / @wesm:
Resolved in #31

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Qian Xu:
I think this is the same issue I have met https://issues.apache.org/jira/browse/ARROW-66 Thanks for fixing this.