Add GLEW dependency to Helper library

GLEW is used by the Helper library files.
Add support for custom CXX_OPTIMIZATION_FLAGS

On my mac, (GCC 4.2.1) the compilation of
SPHFluidSurfaceMapping is failing with "-O2".
Compilation error:
/Users/.../SOFA/modules/sofa/component/mapping/SPHFluidSurfaceMapping.cpp:86: internal compiler error: Segmentation fault: 11
GCC version:
i686-apple-darwin11-llvm-gcc-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.1.00)
Merge branch 'fix-macos10.7-build' into bender-SOFA-1.0

* fix-macos10.7-build:
  Add support for custom CXX_OPTIMIZATION_FLAGS
  Add GLEW dependency to Helper library
Package SOFA

Add install command so SOFA can be packaged with Bender. Note that SOFA
doesn't package Qt yet.

Not tested on mac.