Fixed locally defined but not unused typedef warnings on GCC.

Passes tests.
Merge pull request #2 from DanielaE/feature/qoi-warnings

Suppress msvc level-4 warnings.
Added test for bug #5041 - %y in single digit year

Ahmed Charles: Tests pass with MSVC 2013.
Clarified the docs and examples for previous_weekday and next_weekday. Refs #5753.
Merge branch 'develop' of github.com:boostorg/date_time into develop
#else/#endif comments are updated accordingly to the used condition

Fixed incorrect comments for the condition at the next line:
#if defined(BOOST_DATE_TIME_HAS_REENTRANT_STD_FUNCTIONS)
There were later:
#else // BOOST_HAS_THREADS
#endif // BOOST_HAS_THREADS
It prevented a proper fast undesrstanding of the source.
Merge pull request #8 from mingulov/patch-1_1

#else/#endif comments are updated accordingly to the used condition
remove unused variable in tz_db_base::load_from_file()
Merge pull request #10 from maksqwe/unused_fix

Remove unused locale variable