JavaCL/Blas: integrate @fvlankvelt's patch

Block multiplication doesn't work on CPU, when maxWorkItemSizes < 16x16.
Reintroduced old, naive multiplication code as a fallback, and
introduced stride and blockSize throughout the matrix code (default
block size is defined in CLDefaultMatrix2D. DEFAULT_BLOCK_SIZE).
Merge branch 'master' of github.com:ochafik/nativelibs4java into fvlankvelt-integ