gnat_rm.texi: Update overflow description.

gnat_rm.texi: Update overflow description.

2012-12-05  Robert Dewar  <dewar@adacore.com>

	* gnat_rm.texi: Update overflow description. Pragma Overflow_Checks
	changed to Overflow_Mode.

2012-12-05  Robert Dewar  <dewar@adacore.com>

	* checks.ads, exp_ch4.adb, gnat1drv.adb, par-prag.adb, sem_prag.adb,
	snames.ads-tmpl, switch-c.adb, types.ads, checks.adb: Change pragma
	Overflow_Checks to Overflow_Mode.
	Separate overflow checking from overflow mode.
	Several name changes to reflect this separation.
	CHECKED mode is renamed STRICT mode.

From-SVN: r194193