add lint check for functions with Caffe alternatives (memcpy, memset)

...and other small changes:

* lint output targets depend on `scripts/cpp_lint.py` itself so that lint is rerun when the script is modified (doubt anyone but me cares about this..)
* added `caffe_memset` and `caffe_gpu_memset` functions (analogous to `caffe_{,_gpu}_memcpy`) to replace remaining calls to `memset` (e.g., in syncedmem)