Filter and FileProject support for extended properties.

* Added support for extended properties to `Filter`. Unlike the basic
  properties, which allow the caller to specify a list of acceptable values, the
  extended properties only supports a map of properties, all of which must be
  available on the issue and match the given value.
* Made `Issue` a concrete class. There was no reason it could not be a concrete
  object. The main difference is that the extending classes all add some sort of
  persistence to the issue, but having an in-memory `Issue` in its most basic
  form can be useful and should be allowed.
* Changed the default priority for new issues from 9 to 5.
* Bug fix on `FileIssue.formatIssue()`. If was not properly returning its
  result leading to failure if no extended properties were given.
* Reworked `FileIssue.formatIssue()` to only print the horizontal rule
  seperating the issue text from the extended properties if there are extended
  properties to print as well.
* Changed the `FileProject.createNewIssue()` to handle extended properties and
  handle the basic properties in a manner more consistent with `Issue`. It is
  now creating an `Issue` object and using the `FileIssue.formatIssue()`
  function to write that to a new issue file, then loading that file back in as
  a `FileIssue`. This cuts down on code duplication and makes it so that the
  options map that `FileProject.createNewIssue()` expects is the same as the
  options to the `Issue` constructor.

libpit/project.properties

@@ -1,11 +1,11 @@
-#Wed, 07 Dec 2011 17:53:14 -0600
+#Thu, 08 Dec 2011 14:35:45 -0600
 #Sat Apr 24 17:08:00 CDT 2010
 build.dir=build
 src.dir=src
 lib.shared.dir=../shared-libs
 test.dir=test
-build.number=8
-version=3.1.0
+build.number=10
+version=3.2.0
 name=libpit
 lib.dir=lib
 lib.local=true