Partial fix for issue 127: IWYU and static members.
Static members are now detected as always forward-declarable.
Issue 127 has another problem with macros, but I believe this is a good
independent first step.

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@538 812d1f90-f944-d88a-411a-122bdc93e1ea
Fix issue 126: Precompiled-headers support with --prefix_header_includes
IWYU now supports a new --pch_in_code switch which indicates the first
include directive in the translation unit is a precompiled header.
Precompiled headers are treated as prefix headers, even though they
were not specified on the command-line, but they can never be removed.
Finally, they sort first in include lists generated by IWYU, because
most compilers require the PCH to be included before anything else.

git-svn-id: http://include-what-you-use.googlecode.com/svn/trunk@539 812d1f90-f944-d88a-411a-122bdc93e1ea