gnat_ugn.texi (Conventions): List environment variables and metasyntactic variables.

gnat_ugn.texi (Conventions): List environment variables and metasyntactic variables.

* gnat_ugn.texi (Conventions): List environment variables and
metasyntactic variables.
(Compiling Programs): Fix notation of metasyntactic variables.
Add @file where appropriate.  Use @file for file extensions,
@samp for strings.
* gnat_rm.texi, gnat_ugn.texi: Where appropriate, use @samp
instead of @file, @env instead of @code.

From-SVN: r132641