InputParser and ParseBuffer requires pthread
check if it's available
Add basic unit test for StreamingDenseFeatures reading
Fix Example<T> in ParseBuffer.h
instead of trying to store the example as SGVector<T> in an Example<T>
rather store it as T* as T can be SGSparseVectorEntry.
Use SG_REALLOC instead of SG_MALLOC in StreamingAsciiFile when reading
sparse vectors, this way enabling true buffering in ParseBuffer
Add example_reading_from_features to StreamingDenseFeatures unit test
Merge branch 'feature/FixStreaming' into develop
Merge pull request #1580 from ZhengyangL/feature/mldatafile

add unit-test to simple mldata downloader / fix the indent / make url_prefix configurable
don't fail when curl is not available
combine #IFDEFs and fix little ident mistakes