resolve stability issue caused by non-atomic reference count in shared_array<> class
speedup parsing of messages that contain a lot of repeating groups
speedup FieldBase::calculate() method which improves message encoding/decoding
Remove group counter field when last group of specific type is removed from message
Remove excessive dictionary lookups during message parsing
Merge pull request #1 from Ambal/master

Patches from Quickfix Tickets 23, 24, 26, 27, 28