implement pre_advance event

pre advance event fires before the user sees the advancement dialog.
Implements fr https://gna.org/bugs/?21464
Merge pull request #264 from gfgtdf/preadvance

implement pre_advance event (https://gna.org/bugs/?21464)
updated Lithuanian translation
updated Slovak translation
Set travis back to the usual, nonsegfaulting configuration for gcc

This reverts commit c9c75e9933c2b94cd7a965200eae42970b541867.
and commit c9c75e9933c2b94cd7a965200eae42970b541867
wmltools GUI: remove -f and -p wmllint options, add -m
SConstruct: Use full condition evaluation when checking dependencies