const char* matrix ordering

[zhifeng sheng]

Dear Petsc-developer

I found MatOrderingType is defined as

#define MatOrderingType char*

therefore, g++ complains with a warning when I do something like

MatOrderingType x = MATORDERING_ND

....So, I don't know whether it should be defined as

#define MatOrderingType const char*

Best regards
Zhifeng