Created lru cache using the groupcache/lru package.
Added missing cluster configuration option to adjust the size of the cache.
Moved preparedLRU definition to cluster.go as it seems more fitting. Reduced scope of locking for the prepared statement cache in the error handling code when executing batch statement. Improved the test cases.
Extended the TestPreparedEviction test to include testing the accuracy of the cache eviction process.
Refactored test code so a single test is used to validate the LRU functionality.
Added a test to verify the bug described by #191
Introduce handling for query argument length mismatches
Removed extraneous query args that cause the test to fail now that the arg length is being checked
Changed test code from t.Errorf to t.Fatalf to fail fast.
Split test out into separate tests for too few and too many query args
Fixed some typos and gave a test a better name
Removed unnecessary continue statement in test.
Merge pull request #190 from phillipCouto/prepared_lru3

Added LRU Cache for Prepared statements to prevent memory leaks
Merge upstream master
Added query args length check to batch statements
Merge pull request #192 from relops/verify_query_arg_length

Prevent query argument length mismatches causing a panic