There is no need to say "with P;" in package P.Q.  This patch adds a
warning for that case.

We also remove with clauses in our own code that trigger the warning.

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

gcc/ada/

	* sem_ch10.adb (Check_Redundant_Withs): Add a warning if a
	library unit with's its own ancestor. Note that this warning is
	not triggered for something like "with P.R;" in P.Q, because
	there the "with P;" is considered implicit.
	* fname-sf.adb, libgnarl/s-stusta.adb, libgnarl/s-tasdeb.ads,
	libgnat/a-calfor.adb, libgnat/a-tiboio.adb,
	libgnat/a-wwboio.adb, libgnat/a-zzboio.adb, libgnat/i-cobol.adb,
	libgnat/s-bitops.adb, libgnat/s-bitops.ads,
	libgnat/s-direio.adb, libgnat/s-dwalin.adb,
	libgnat/s-geveop.adb, libgnat/s-mmosin__unix.adb,
	libgnat/s-os_lib.adb, libgnat/s-os_lib.ads,
	libgnat/s-pooglo.ads, libgnat/s-secsta.adb,
	libgnat/s-shasto.adb, libgnat/s-stausa.ads,
	libgnat/s-stratt.ads, libgnat/s-ststop.adb: Remove with of
	parent.
	* sinfo.ads: Minor comment fix.