Merge pull request #169 from stuarteberg/blocked-iterator-mac-fixes

Blocked iterator mac fixes
fixed file resize for VIGRA_NO_SPARSE_FILE
added multi-threaded test for ChunkedArrayTmpFile
cmake: added compiler flags to run the multi-threaded chunked array test
restored test/multiarray/test.cxx (chunked tests are now in test/multiarray/test_chunked.cxx)
cmake: don't specify additional gcc flags when MSVC is used
test/multiarray/CMakeLists.txt: On Mac, use -stdlib=libc++