1) Require libxml-2 and build new file preset_xml.c

2) In effects.c, some EffectsValues are changed to better reflect the
   strings used in the XML.

3) New EffectSettings are added for use when writing out effects to XML.

4) Added an XmlLabel structure for mapping a value to a string. Generally,
   these are the union of the set of all values over the set of supported
   devices.

5) There's a large array of XmlSettings used to derive the translation of
   a preset to XML.

6) Add an enum for product_id and use it to set a filter for file suffix.

7) Minor cleanup in push_message() that suppresses spurious error messages.

8) Fixed a bad memset in read_data_thread().

9) In gdigi.h, a few changes in names to be consistent with XML.

   There are some new definitions of LFO and VSWITCH parameters that
   need to be computed.

10) In gui.c, fixed up a compiler warning.

    Added a map from device id to file type and code to set a default filter
    in the read dialog.

    Wired up the 'save to XML' callback and reorganized the menue entries to
    better distinguish between 'save to file' and 'store to device'.

   In preset.c, sort the params so that what we write as XML more closely
   matches what is generated on the windows side.

effects.h

@@ -19,7 +19,7 @@
 
 #include <glib.h>
 
-enum {
+typedef enum {
   VALUE_TYPE_PLAIN  = 0,      /**< value displayed directly */
   VALUE_TYPE_SUFFIX = 1 << 0, /**< use suffix for displaying */
   VALUE_TYPE_OFFSET = 1 << 1, /**< use value offset */
@@ -27,6 +27,7 @@ enum {
   VALUE_TYPE_LABEL  = 1 << 3, /**< use value labels (overrides any other option) */
   VALUE_TYPE_EXTRA  = 1 << 4, /**< use extra values */
   VALUE_TYPE_DECIMAL= 1 << 5, /**< display decimal places */
+  VALUE_TYPE_NONE   = 1 << 6, /**< no value displayed */
 } ValueType;
 
 typedef struct _EffectValues {
@@ -93,6 +94,18 @@ typedef struct {
     PresetBank bank;
 } Banks;
 
+enum product_id {
+   RP150    = 1,
+   RP250    = 2,
+   GNX4     = 3,
+   GNX3000  = 4,
+   RP500    = 5,
+   RP1000   = 6,
+   RP155    = 7,
+   RP255    = 8,
+   RP355    = 9,
+};
+   
 typedef struct {
     gchar *name;
     unsigned char family_id;