Fix issue 159: Don't instantiate deleted methods.

Now check that implicit methods are not deleted before attempting to
instantiate them. Add a single test file to capture the constructs we used
to crash on.

Original patch by SmSpillaz.

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@589 812d1f90-f944-d88a-411a-122bdc93e1ea