Const correctness2

[AerysL]

This improves the const correctness of EVSL. Useful for reasons such as

It protects you from accidentally changing variables that aren't intended be changed,
It protects you from making accidental variable assignments, and
The compiler can optimize it. 
For instance, you are protected from
if( x = y ) // whoops, meant if( x == y )

as per https://stackoverflow.com/questions/136880/sell-me-on-const-correctness

[liruipeng]

@AerysL This makes sense to me. We did not pay much attention on the use of keyword "const".

It seems like C++ is more strict on this than C. E.g., C allows mismatch between "const type *" and "type *" used in function prototypes and functions, but C++ does not.

Please try to build with C++. Do "./configure --with-cxxcompiler" and "make -j test", and check if there is something missed.

Nice work. Thanks!

[AerysL]

Good catch, the errors specifically are due to the fact that the reference BLAS implementation (and apparently some other BLAS implementations as well) don't declare const correctness correctly. I used the definitions used by MKL's implementation (which appears to be the same as the OpenBLAS implemenation).
The way to handle this is to use C++'s const_cast. I think the best way to handle this is probably to provide a section which, when compiled with evsl, defines evsl_blas to be a wrapper functions around the desired blas call with const_cast applied correctly. Does this sound reasonable to you?