Fix seg fault on overloaded connection (CPP-167)

Improper static cast and use of pointer in timeout callback
Also removed unused parameter in Pool::maybe_notify_ready()
Add NULL check to cass_value_get_*
Updating the NULL test case to check for CASS_ERROR_LIB_NULL_VALUE when using the appropiate cass_value_get*() function
Update basics.cpp
Merge pull request #75 from datastax/CPP-165-itest

Updated NULL (Basics) Integration Test for CPP-165