First version of degeneracy based maximum cliques, adjlists are not optimized yet.

Conflicts:
	src/Makefile.am
Improving maximal cliques, sort adjacency lists, it is slower now, temporarily.
Version with adjlists. Slooooooow. Speeding up now.
Only order adjacency lists for pivoting.
This is fast, but need to check an assumption, see TODO in source.
Fixed memory handling issues.
Two minor speedups.
More minor speedup using some pointer arithmetic.
Only reorder if there is a pivot selection at the next level.
Merging reordering and pivot selection, speedup.
Merge branch '0.7-graphlets' of github.com:igraph/igraph into 0.7-graphlets