Exclude aliases from lex_utils missing-lang.txt files

[a2line]

Lexicon entries that are aliases should be excluded from the “langage empty line extraction” process. We don’t need translation for them.

    cousin.0.2
->: a grandson/a granddaughter/a grandchild

    cousin.0.2
de:

They are quite easy to track because there is no translation support at all for them. I have done a manual pass on current missing-lang.txt files.

[hgouraud]

should be fixed by my last commit (d249b14)

there is still a problem with
Fatal error: exception Compenv.Exit_with_status(0)
I will discuss it with OcamlPro this coming Friday