This change introduces new literals B75, B110, B150, B300, and B600 for
enumerated type GNAT.Serial_Communications.Data_Rate, denoting the
corresponding bit rates. This allows communication with legacy devices
that require them.

Tested on x86_64-pc-linux-gnu, committed on trunk

2015-05-12  Thomas Quinot  <quinot@adacore.com>

	* g-sercom.ads, g-sercom-linux.adb (GNAT.Serial_Communications.
	Data_Rate): New literals B75, B110, B150, B300, B600.