Update to reflect changes in Clang.

DefaultImageName from the Driver constructor was eliminated in Clang r208926.

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@545 812d1f90-f944-d88a-411a-122bdc93e1ea
Fix a few typos in comments.  No functional change intended.

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@546 812d1f90-f944-d88a-411a-122bdc93e1ea