[Ada] move some warning to style check

[Arnaud Charlet <charlet at adacore dot com>]

Tested on x86-linux, committed on mainline.

The warning for a C-style extra level of parentheses around conditionals
is now a style warning (controlled by the -gnatyx switch, and included
by default in -gnaty), rather than being a redundant construct warning.
On reflection, this is really more of a style issue, and since this
imported-from-C style is more common than it should be in Ada programs,
it is useful to be able to control it separately from the other useful
redundant construct warnings. While we are at it, the name of the flag for
subprogram ordering is changed from Subprogram_Order to Order_Subprograms
since this corresponds better to its alpha switch letter (which is o).

2004-11-18  Robert Dewar  <dewar@adacore.com>

	* errout.ads, errout.adb: (First_Sloc): New function

	* par-ch5.adb (P_Condition): Check for redundant parens is now a style
	check (-gnatyx) instead of being included as a redundant construct
	warning.

	* sem_ch6.adb: Change name Style_Check_Subprogram_Order to
	Style_Check_Order_Subprograms.

	* style.ads, styleg.ads, styleg.adb, styleg-c.adb, stylesw.ads,
	stylesw.adb: Add Style_Check_Xtra_Parens

	* usage.adb: Add line for -gnatyx (check extra parens)

	* vms_data.ads: Add entry for STYLE_CHECKS=XTRA_PARENS => -gnatyx

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