configure: Fix Graphviz test and input generation.

This check for Graphviz never actually worked properly because Autoconf
swallows up the [] around [gG], so Graphviz was always detected as missing.
This commit fixes the problem by doubling up to [[gG]].

Because Graphviz was never used, I never noticed that ovsdb-dot had not
been revised to use the latest Python interface to OVSDB, so this commit
fixes up those problems too.

m4/openvswitch.m4

@@ -198,7 +198,7 @@ AC_DEFUN([OVS_CHECK_DOT],
     [for dot],
     [ovs_cv_dot],
     [dnl "dot" writes -V output to stderr:
-     if (dot -V) 2>&1 | grep '^dot - [gG]raphviz version' >/dev/null 2>&1; then
+     if (dot -V) 2>&1 | grep '^dot - [[gG]]raphviz version' >/dev/null 2>&1; then
        ovs_cv_dot=yes
      else
        ovs_cv_dot=no

ovsdb/ovsdb-dot.in

@@ -1,6 +1,8 @@
 #! @PYTHON@
 
 from datetime import date
+import ovs.db.error
+import ovs.db.schema
 import getopt
 import os
 import re
@@ -9,18 +11,18 @@ import sys
 argv0 = sys.argv[0]
 
 def printEdge(tableName, baseType, label):
-    if baseType.refTable:
+    if baseType.ref_table:
         options = {}
         options['label'] = '"%s"' % label
-        if baseType.refType == 'weak':
+        if baseType.ref_type == 'weak':
             options['constraint'] = 'false'
         print "\t%s -> %s [%s];" % (
             tableName,
-            baseType.refTable,
+            baseType.ref_table,
             ', '.join(['%s=%s' % (k,v) for k,v in options.items()]))
 
 def schemaToDot(schemaFile):
-    schema = DbSchema.fromJson(ovs.json.from_file(schemaFile))
+    schema = ovs.db.schema.DbSchema.from_json(ovs.json.from_file(schemaFile))
 
     print "digraph %s {" % schema.name
     for tableName, table in schema.tables.iteritems():
@@ -73,7 +75,7 @@ if __name__ == "__main__":
 
         schemaToDot(args[0])
 
-    except Error, e:
+    except ovs.db.error.Error, e:
         sys.stderr.write("%s: %s\n" % (argv0, e.msg))
         sys.exit(1)