Fix udunits on mac / travis

[alliepiper]

PR #847 updated the udunits version and removed the patch that fixed compilation on Travis's mac boxes (the failing flex issue, #769).

Either update the udunits compilation to use the new CMake support, or reapply the flex patch.

[alliepiper]

@aashish24 Their CMake system won't work -- it doesn't install the udunits.h header, which is needed by UVCDAT/Packages/unidata to build the python udunits interface.

I'll remake the patch for their configure script.

[doutriaux1]

@dlonie I thought @jbeezley just updated their cmake to use 3.1 I guess the brew version is broken then?

If so it might be worth further editing @jbeezley patch to simply build CMake like we do for Linux?

[jbeezley]

I think he is referring to the CMakeLists.txt file provided by udunits.

[alliepiper]

It's a problem with the way the udunits package has written their CMake build system -- it doesn't install the same files as their autoconf script does.