Using wordexp() instead of replace_tilde(), to pick up homedir and other

enviornment variables (under Linux only).
All C++-style comments replaced with C-style.

docs/CHANGES.txt

@@ -8,7 +8,7 @@ http://www.tuxpaint.org/
 
 $Id$
 
-2008.October.7 (0.9.21)
+2008.October.8 (0.9.21)
   * New Starters:
     -------------
     * Silver Frame
@@ -68,6 +68,14 @@ $Id$
     * "Negative", "Tint", "Glass Tile", "Darken" and "Lighten" tools
       can all now affect the entire image.
 
+  * System-Related Improvements:
+    ----------------------------
+    * 'savedir', 'datadir', 'printcommand' and 'altprintcommand' options in
+      configuration files (e.g., ~/.tuxpaintrc) now expand environment
+      variables and tildes (e.g., "~" for $HOME, or "~username" for 'username's
+      home directory) on Linux.  (Using 'wordexp()')
+      NOTE: Environment variable expansion not yet supported on other platforms.
+
   * Build System Improvements
     -------------------------
     * Adhering to Debian & FreeDesktop.org standards regarding .desktop file.