err_str passed as far as gpuarray.pyx and PRINTED
Using strb for much cleaner code.  Now Raising *err_str
(Potentially) more idiomatic strb usage
Append an extra \0 for safety
Line-numbered source in error message for CUDA kernels too
Tidying code
len now size_t, and (possibly) final touches
Comment made less like actual code
Merge pull request #28 from mdda/cl-kernel-debug

err_str passed as far as gpuarray.pyx and PRINTED (Issue #27)
Add #ifdef sauce to avoid warnings in release mode.