Use 'dumb quotes' rather than `really dumb quotes'

Back in the far-off twentieth century, it was normal on unix
workstations for U+0060 GRAVE ACCENT to be drawn as "‛" and for U+0027
APOSTROPHE to be drawn as "’". This led to the convention of using
them as poor-man's ‛smart quotes’ in ASCII-only text.

However, "'" is now universally drawn as a vertical line, and "`" at a
45-degree angle, making them an `odd couple' when used together.

Unfortunately, there are lots of very old strings in glib, and also
lots of new strings in which people have kept up the old tradition,
perhaps entirely unaware that it used to not look stupid.

Fix this by just using 'dumb quotes' everywhere.

https://bugzilla.gnome.org/show_bug.cgi?id=700746

glib/gutils.c

@@ -424,9 +424,9 @@ g_find_program_in_path (const gchar *program)
 #if defined(G_OS_UNIX) || defined(G_OS_BEOS)
   if (path == NULL)
     {
-      /* There is no `PATH' in the environment.  The default
+      /* There is no 'PATH' in the environment.  The default
        * search path in GNU libc is the current directory followed by
-       * the path `confstr' returns for `_CS_PATH'.
+       * the path 'confstr' returns for '_CS_PATH'.
        */
       
       /* In GLib we put . last, for security, and don't use the
@@ -510,7 +510,7 @@ g_find_program_in_path (const gchar *program)
 
       if (p == path)
         /* Two adjacent colons, or a colon at the beginning or the end
-         * of `PATH' means to search the current directory.
+         * of 'PATH' means to search the current directory.
          */
         startp = name + 1;
       else