Replace POSIX directory operations by Boost Filesystem

[gjasny]

To support compiling the generate_geocoding_data generator on non-POSIX systems like Windows I replaced the POSIX code with Boost Filesystem. After the change the generator produes exactly the same output as before. This should close Issue #824.

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This change is 

[andyst]

@hagbard @roubert for added C++ and Windows (kidding) expertise.

[andyst]

This doesn't look right to me.
We can't replace "USE_BOOST" check with "USE_BOOST OR BUILD_GEOCODER" when the check is guarding includes for Boost headers.

[andyst]

I take this back. In this context this is doing the right thing. My initial reading was wrong.

[andyst]

Still need to review the rest of the code. Just added an initial comment.

[andyst]

@roubert could you please take a look at this CL in terms of C++?
Looks good to me but maybe you spot something.

[andyst]

This code needs to continue to work without Boost.

Please follow the pattern in https://github.com/googlei18n/libphonenumber/blob/master/cpp/src/phonenumbers/base/memory/scoped_ptr.h to use Boost "#if defined(I18N_PHONENUMBERS_USE_BOOST)" and fall back to the current code based on dirent.h.

[ginggs]

line 58 of tools/cpp/CMakeLists.txt
should be:

target_link_libraries (generate_geocoding_data_test ${TEST_LIBS} ${Boost_LIBRARIES})

instead of:

target_link_libraries (generate_geocoding_data_test ${TEST_LIBS})

so that generate_geocoding_data_test also gets linked with Boost

[keghani]

Hi @gjasny,

Are you interested in / able to help us get this PR merged in the foreseeable future?
Sorry Windows hasn't seen much love lately, but we don't actively maintain Windows builds and couldn't test such a PR.
If someone else in the open-source community (@ginggs? Thanks for helping review too!) could test it out and help with the review we'd accept it.

Related issues in case anyone could help collaborate there:

• #1555, to allow Windows to build cpp library with pthreads for multi-threading (would this still be an issue after this PR?)
• #1307, to use readdir instead of readdir_r

[keghani]

This is infeasible given the lack of reviewers or a response.

We don't actively maintain windows builds and we'd need someone else in the open-source community to test and help review this PR. Please see the known Windows issues, maybe someone else there or in the
discussion group could help.