unifdef: do not mark the line as dirty when there is no dirt

This caused problems for #undef directives in -f header files:
the following line was ignored because the line state got
incorrectly updated.

Thanks to the uClibc project for reporting the bug and providing a
sample test case and a proposed fix.

Reported-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
bump more copyright dates
web: update for unifdef-2.10 release