Fix several bugs in BuildCommDCBAndTimeouts:
- make sure LPCSTR parameter is really treated as constant
- fix possible buffer overflow if passed in string is too long
- if the device control string is invalid, do not modify DCB
- do not clear entire DCB, only modify appropriate members
- fix parsing of stop bits parameter so it works for 1 and 1.5
- populate COMMTIMEOUTS when to=xxx parameter is specified
- added support for xon, odsr, octs, dtr, rts, and idsr parameters
- fix several other parsing errors