This is a preliminary internal change for setting Do_Discriminant_Check
flags properly in the tree. No functional effect, so no test needed

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

2014-01-21  Robert Dewar  <dewar@adacore.com>

	* sinfo.ads, sinfo.adb: Change Do_Discriminant_Check to use new Flag1.
	Add this flag to type conversion nodes and assignment nodes.
	* treepr.adb: Deal properly with Flag 1,2,3.
	* treeprs.adt: Minor comment update.