fix: parent relative paths, and rework on the whole path extraction mechanics

[Tal500]

• Include also another integration test function to check header in parent dir usage (that was failing in previous commit).
• Add a safety check that we did not meet the header file that we are about to insert to the map (abort with stderr message otherwise) - this not only detect unmet bugs in including paths, but also avoid memory leak.
• Add much more cover in the test functions, and check more details.

[danmar]

some comments. I didn't check it all carefully yet.

[danmar]

small question. partial review.

[Tal500]

I read your comments and reply in the code context.
I do think that even if you want to have a fine graded internal testing, you shall first merge this PR and introduce in a new PR the new extra internal unitest system.