UDUNITS-2 Cmake/Visual Studio build broken.

[WardF]

In the course of answering a question re: UDUNITS-2 Issue #16, I've discovered that the latest code in master fails to compile on Windows with Visual Studio. The culprit is the auto-generated file scanner.c, which has introduced a dependency on unistd.h. This issue is clearly known on other platforms, as a lack of unistd.h has been mitigated in autotools-based builds.

The fix should be fairly simple; I forked and took a quick pass, but the fix I added didn't work as expected. I will pursue as best I can, although my focus right now is on some netcdf-c issues.

[ocefpaf]

@WardF it will be awesome to get rid of a bogus dependency. Meanwhile we are building on windows by copying an empty file named unistd.h to the build directory.

(See https://github.com/ocefpaf/conda-recipes/blob/master/udunits2/bld.bat#L14)

[WardF]

I've addressed this issue in #41. I don't have access to merge the pull request, and even if I did, the project maintainer is @semmerson so I'd want him to review it first. But, once reviewed, it can be merged.

The changes were tested in Windows 10 (64-bit) with Visual Studio 12. Testing was also performed on the latest OSX, and a Ubuntu 15.10 environment.

[semmerson]

Looks good. I merged and pushed to GitHub. Hopefully, a new release will be out by COB tomorrow.