Fix bugs in unit tests

[pakmarkthub]

Problems:

• namespace gdrcopy::test { ... } syntax is not supported in GCC 4.8.
• ck_assert_int_eq cannot be used with pid_t on libcheck v0.9.8.

This PR:

• changes the namespace definition to namespace gdrcopy { namespace test { ... } } for backward compatibility.
• uses ck_assert with pid_t instead.