+ Adds a specification for the new ldap extensible filter

I am not sure about this, since I haven't been able to find
documentation about what this does. This should work, though.

Cleanup of comments and exceptions, adds specification for
Filter.ex and a parser method.

spec/unit/ldap/filter_spec.rb

@@ -0,0 +1,48 @@
+require 'spec_helper'
+
+describe Net::LDAP::Filter do
+  describe "<- .ex(attr, value)" do
+    context "('foo', 'bar')" do
+      attr_reader :filter
+      before(:each) do
+        @filter = Net::LDAP::Filter.ex('foo', 'bar')
+      end
+      it "should convert to 'foo:=bar'" do
+        filter.to_s.should == '(foo:=bar)'
+      end 
+      it "should survive roundtrip via to_s/from_rfc2254" do
+        Net::LDAP::Filter.from_rfc2254(filter.to_s).should == filter
+      end 
+      it "should survive roundtrip conversion to/from ber" do
+        ber = filter.to_ber
+        Net::LDAP::Filter.parse_ber(ber.read_ber(Net::LDAP::AsnSyntax)).should ==
+          filter
+      end 
+    end
+    context "various legal inputs" do
+      [
+        '(o:dn:=Ace Industry)', 
+        '(:dn:2.4.8.10:=Dino)', 
+        '(cn:dn:1.2.3.4.5:=John Smith)', 
+        '(sn:dn:2.4.6.8.10:=Barbara Jones)', 
+      ].each do |filter_str|
+        context "from_rfc2254(#{filter_str.inspect})" do
+          attr_reader :filter
+          before(:each) do
+            @filter = Net::LDAP::Filter.from_rfc2254(filter_str)
+          end
+
+          it "should decode into a Net::LDAP::Filter" do
+            filter.should be_an_instance_of(Net::LDAP::Filter)
+          end 
+          it "should survive roundtrip conversion to/from ber" do
+            ber = filter.to_ber
+            Net::LDAP::Filter.parse_ber(ber.read_ber(Net::LDAP::AsnSyntax)).should ==
+              filter
+          end 
+        end
+      end
+    end
+  end
+  
+end