Handle macros and placement operator new in prefix headers (issue #125).

Keep FileEntry for the files defining macros, find FileEntry by quoted include
for placement operator new.

Known problems: added 2 tests fail on Windows due to issue #129 "Unused
templates are ignored on Windows".

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@537 812d1f90-f944-d88a-411a-122bdc93e1ea