Check to see if 'cb' exists in 'close()' before calling it
Attempt to handle INVALID_HANDLE errors
Added some comments
Merge branch 'infinite_loop' of https://github.com/theduderog/node-odbc into test-merge
Add test for pull request issue
Close result objects in columns and tables proxy functions
Add a debug message
Add an assertion that return value from SQLGetData must not be -2
Updated most recent issue test
Merge branch 'v0.5' into test-merge
Move assertion to inside error handling and attempt to throw an error object

This could be bad because are in some cases expecting to pass
the error object back as an argument to the callback function.
Other times it might be ok to actually throw. At any case, this
should be a super rare error to hit.
0.5.26