Configtool: ignore value options in board.metadata.

This solves the problem of choice menus being populated with too
many entries. Before, such menus would pick up values from
board.metadata as well as from the actually loaded file.

File printer.metadata contains no options, so no adjustment
needed there.

configtool/boardpanel.py

@@ -294,6 +294,13 @@ class BoardPanel(wx.Panel):
       elif ln.lstrip().startswith("#define"):
         self.parseDefineName(ln)
 
+    # Ignore candidates in the metadata file.
+    self.candHeatPins = []
+    self.candThermPins = []
+    self.candProcessors = []
+    self.candClocks = []
+    self.tempTables = {}
+
     prevLines = ""
     for ln in self.userBuffer:
       if ln.rstrip().endswith("\\"):