Updated serial modules for supporting Ingenico devices.
* i6550 supports serial devices. May work on non-Windows
* RBA_USB should eventually derive more from i6550 since
  the messaging and logic ought to be identical.
* Other files changed to reduce compliation warnings.
i6550 is the closest to complete but not quite done. POS side
does not support MSR encryption format. Sig Capture not
tested.
Parsing support for Ingenico-formatted e2e blocks
Renamed SPH_Ingenico_i6550 to SPH_IngenicoRBA_RS232 since all RBA
devices should be able to use it. Did some refactoring so that
RBA_USB and RBA_IP can inherit most functionality from RBA_RS232
with the child classes just reponsible for low-level differences
in reading/writing bytes from the network vs different types of
devices.