Change all quotes in strings and comments to the new GNU standard.

The asymmetric quotes used by GNU in the past (`...') don't render
nicely on modern systems.  We now use two \x27 characters ('...').

The proper solution would be to use the correct Unicode symmetric
quotes here.  However this has the disadvantage that the system
requires Unicode support.  We don't want that today.  If Unicode is
available a generated po file can be used to output proper quotes.  A
simple sed script like the one used for en@quote is sufficient to
change them.

The changes have been done by applying

  sed -i "s/\`\([^'\`]*\)'/'\1'/g"

to most files and fixing obvious problems by hand.  The msgid strings in
the po files were fixed with a similar command.

dirmngr/ldap-url.c

@@ -49,7 +49,7 @@ Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that this notice is preserved.
 The names of the copyright holders may not be used to endorse or
 promote products derived from this software without their specific
-prior written permission.  This software is provided ``as is''
+prior written permission.  This software is provided `'as is''
 without express or implied warranty.
 
 ---
@@ -62,7 +62,7 @@ provided that this notice is preserved and that due credit is given
 to the University of Michigan at Ann Arbor.  The name of the
 University may not be used to endorse or promote products derived
 from this software without specific prior written permission.  This
-software is provided ``as is'' without express or implied warranty.  */
+software is provided `'as is'' without express or implied warranty.  */
 
 
 #include <config.h>