[Bug-gsl] Possible error handling/return bug in vector/copy_source.c

[Diego]

I've been playing with a wrapper for GSL for Chicken Scheme and I've found what 
I believe might be a bug in the file vector/copy_source - do let me know if 
I've missed something, because I'm extremely new to this code base. In 
FUNCTION(gsl_vector, memcpy), the logic that checks that the length of the 
vectors is equal falls under the #else clause.

This means that (especially with no error handler set, as is recommended for 
production code) if one of the other #if clauses is triggered during 
compilation, memcpy will call a blas copy function instead, and can (and will) 
fail silently - it calls the blas version /without/ returning, and then goes on 
to unconditionally return GSL_SUCCESS. (In contrast, the memcpy in 
matrix/copy_source.c checks the lengths before going into the #if/blas logic).

For the proper errno codes to be returned, I would propose that either: a) the 
vector length check and GSL_ERROR call should be before the first #if, as in 
matrix/copy_source.c or b) each clause that ends up calling a blas function 
should be using e.g. `return gsl_blas_dcopy(...)` so that the proper error 
codes are returned. I think option a would be preferable for consistency and so 
as to not have to rely on the internals of the gsl_blas API.

- Diego