Remove self comparisons in test/extern/ferguson/c_ptrs.chpl

c_ptrs.chpl had comparisons that looked like:

assert(my_ptr == my_ptr);

These now check that my_ptr != c_nil. I added a couple of overloads in
SysBasic to allow comparison between c_ptr and c_void_ptr to let us do
this.
Merge pull request #743 from Kyle-B/kb-remove-self-comparison

Remove self comparisons in test/extern/ferguson/c_ptrs.chpl

c_ptrs.chpl had comparisons that looked like:

assert(my_ptr == my_ptr);

These now check that my_ptr != c_nil. I added a couple of overloads in
SysBasic to allow comparison between c_ptr and c_void_ptr to let us do
this.