[Patch, fortran] PR54679 Erroneous "Expected P edit descriptor" in conjunction with L descriptor

[Jerry DeLisle]

Hi All,

Gfortran currently treats an L format descriptor with no width as an extension. 
When the width is zero (not a positive integer) the error message was confused. 
The checking software was saving the format token, FMT_ZERO, for the next round 
of checks and this was interpreted to be a zero preceding a P edit descriptor.

This is fixed by adding the check for FMT_ZERO explicitly. I also added 
diagnostic messages to better explain the error. L0 is also allowed now as an 
extension.

Regression tested on x86-64-linux. New test case included in patch as well as 
adjusting the text for fmt_l.f90

OK for trunk?

Jerry

2016-10-29  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

	PR fortran/54679
	* io.c (check_format): Adjust checks for FMT_L to treat a zero
	width as an extension, giving warnings or error as appropriate.
	Improve messages.

2016-10-24  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

	PR fortran/54679
	* io/format.c (parse_format_list): Adjust checks for FMT_L to
	treat a zero width as an extension, giving warnings or error
	as appropriate. Improve messages.
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