[patch, fortran] PR34175 Document when fixed form and when free form source code is assumed

[Jerry DeLisle <jvdelisle at verizon dot net>]

I plan to commit the attached patch tomorrow.  Let me know if this is not clear 
enough.  I will include a suitable ChangeLog entry.

Regards,

Jerry
Index: gfortran.texi
===================================================================
--- gfortran.texi	(revision 130392)
+++ gfortran.texi	(working copy)
@@ -374,6 +374,13 @@ and compile it accordingly. A @command{g
 provided, which is identical to @command{gcc} except that it automatically
 links the Fortran runtime libraries into the compiled program.
 
+Source files with @file{.f}, @file{.for}, @file{.ftn}, @file{.F}, @file{.FOR},
+@file{.FPP}, and @file{.FTN} extensions are treated as fixed form.  Source
+files with @file{.f90}, @file{.f95}, @file{.f03}, @file{.F90}, @file{.F95}, and
+@file{.F03} extensions are treated as free form.  The capitalized versions of 
+either form are run through preprocessing. Source files with the lower case
+@file{.fpp} extension are run through preprocessing as well.
+
 This manual specifically documents the Fortran front end, which handles
 the programming language's syntax and semantics.  The aspects of GCC
 which relate to the optimization passes and the back-end code generation
@@ -394,9 +401,9 @@ Fortran compiler.
 @cindex Conditional compilation
 @cindex Preprocessing
 
-Many Fortran compilers including GNU Fortran allow to pass the source code
-through a C preprocessor (CPP; sometimes also called Fortran preprocessor,
-FPP) to allow for conditional compilation. In case of GNU Fortran
+Many Fortran compilers including GNU Fortran allow passing the source code
+through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
+FPP) to allow for conditional compilation. In the case of GNU Fortran,
 this is the GNU C Preprocessor in the traditional mode. On systems with
 case-preserving file names, the preprocessor is automatically invoked if the
 file extension is @code{.F}, @code{.FOR}, @code{.FTN}, @code{.F90},