Fixed PHP-833: Add the MongoClient::killCursor method to kill a cursor on the server

This function is only available on 64-bit platforms. No specific test, as it's
covered by the test for PHP-755.
Fixed test cases' name and collection.
Refactoring handling int64s into its own function.
Fixed PHP-837: Handle cursor IDs for return with MongoCursor::info on 32bit platforms.
Added support for MongoInt64 as 2nd argument to MongoClient::killCursor.
Fixed ZTS mode (again).
Attempt to fix the test case.
Undo extra scoping.
Added test cases to make sure int32/int64's value can not be written to.
Fixed zts again.
Merged pull request #455