R: printing graphs now converts the "name" graph attribute to character.
R: convenience functions to query and set all attributes at once.
R: runtest.sh prints out the working directory, to allow saving the test output.
R: hanle attributes in graph.disjoint.union.
Update union and union_many to return mappings for the edges.
Fixed error handling in _union_many.
R: rewrite graph.union() to handle attributes properly.
Refactor igraph_union.
Refactor igraph_intersection, it can now report edge mappings.
Fixed an igraph_intersection error message.
Temporary.
Update for newer versions of autoconf/automake.

Conflicts:
	configure.in
Merge branch 'develop' into 0.7-ropbyname

Conflicts:
	configure.ac
	interfaces/R/runtest.sh
	src/operators.c
Fix two examples for the new igraph_union API.
R: fix interface to intersection API changes (#20).
R: fix bracket trick in graph.attributes<- (for #20).
R: transfer new operator tests to testthat (#20).
Another test case for igraph_intersection{,_many}.
Fix igraph_intersection_many bug.
When the first edge was common it was left out.
Fix two typos in igraph_intersection_many error messages.