Problem:    Falling back from NFA to old regexp engine does not work properly.
            (fritzophrenic)
Solution:   Do not restore nfa_match. (Christian Brabandt, closes #867)

Problem:    Can't match "%>80v" properly. (Axel Bender)
Solution:   Correctly handle ">". (Christian Brabandt)

Problem:    Crash when searching for "\ze*". (Urtica Dioica)
Solution:   Disallow a multi after \ze and \zs.

Problem:    A non-greedy match followed by a branch is too greedy. (Ingo
            Karkat)
Solution:   Add NFA_MATCH when it is already in the state list if the position
            differs.

Problem:    Pattern with repeated backreference does not match with new regexp
            engine. (Urtica Dioica)
Solution:   Also check the end of a submatch when deciding to put a state in
            the state list.

Problem:    Using \1 in pattern goes one line too far. (Bohr Shaw, John Little)
Solution:   Only advance the match end for the matched characters in the last
            line.

Problem:    NFA regexp doesn't handle backreference correctly. (Ryuichi
            Hayashida, Urtica Dioica)
Solution:   Always add NFA_SKIP, also when it already exists at the start
            position.

Problem:    Using "\ze" in a sub-pattern does not result in the end of the
            match to be set. (Axel Bender)
Solution:   Copy the end of match position when a recursive match was
            successful.

Problem:    NFA engine does not capture group correctly when using \@>. (ZyX)
Solution:   Copy submatches before doing the recursive match.

Problem:    NFA engine does not match the NUL character. (Jonathon Merz)
Solution:   Ues 0x0a instead of NUL. (Christian Brabandt)