Import lz4 r117rc

 - See http://code.google.com/p/lz4/issues/detail?id=127
Initial implementation of -BD (block dependent) mode.

 - NOTE : This is just a copy from lz4io.c. There is no concurrency.
Add const to MemPool::Buffer::data()
Refactor magic number checking in decompression.
Add srcBits abstraction (EOS, Incompressible)
Refactor atomic quit flag related variable and functions.
Add setting parameter's proxy class Params.
Refactor lz4mtCompressBlockDependency() with Params.
Refactor lz4mtCompress() with Params.
Refactor lz4mtDecompress() with Params.
Refactor lz4mtCompress.
Add readHeader().
Refactor lz4mtDecompress().
Add executables in lz4/programs/ to .gitignore
Update readme.md
Remove redundant "static"
Replace Context pointer with reference.
Rename Context to Ctx.
Rename ctx to lz4MtContext.
Refactor Ctx::writeU32()