some C99 quirks fixed in lad.c; more to come
cleaned up igraph_i_lad_updateMatching as well
more fixes to the LAD isomorphism algorithm to make it C89-compliant
LAD compiler issues mostly fixed; also, better error handling was implemented
LAD isomorphism search fixed to actually compile in MSVC
Merge branch 'feature-fix-lad-msvc' into develop
Merge branch 'develop' of github.com:igraph/igraph into develop