Fixes 'No newline at end of file' message appearing in unexpected places. Problem noticed by op@

This restores the traditional diff -p behaviour in Got.

Contains new APIs for chunk offset retrieval.

Brings in improved accuracy of function prototypes in hunk headers.

This fixes a scrolling problem in tog's diff view for diffs which contain lines of the form "Binary files %s and %s differ".

This new diff implementation was started by Neels Hofmeyr during the u2k20 hackathon and now replaces diffreg.c code lifted from the OpenBSD base system. The integration of this code into Got was done by me. Got now uses the patience diff algorithm by default. The diff.git repository will remain the primary repository for the diff code, which already compiles and runs on other operating systems such as Linux. Any fixes and improvements for files inherited from the diff.git repository should be written against that repository and synced to got.git afterwards.