exclude include/ so will remove /usr/local/include too

also add a hack to change the paths to be consistent
in the case that the directory the job is done in is a symlink
to another directory.
(Alternative method would be to run the lcov tool multiple times
for each path and set the base-directory switch plus add-tracefile
switch to combine.)

I didn't get this reviewed. I am under assuption that this make target
is rarely used.