Validation: catch syntax errors?

[fingolfin]

Sometimes packages do stuff that causes syntax errors to be printed, but GAP carries on. E.g. this warning (fixed in this PR):

gap> LoadPackage("lpres":OnlyNeeded);
Syntax warning: Unbound global variable in /Users/mhorn/Projekte/GAP/gap/pkg/lpres/read.g:22
    return( ACECosetTable( f, rels, gens : silent, hard, max := 10^8, Wo := 10^8 ) );
            ^^^^^^^^^^^^^
Loading lpres 1.0.1 ...
true

On the one hand, this warning is harmless. On the other hand it is spooky and scary and user should not have to see it, so it'd be nice to catch it, so that we can notify upstream others about it.

Not sure how to test achieve this, though. Perhaps GAP needs a --strict option which turns syntax warnings into errors?