- include config.h instead of manually adding -DHAVE_{CPLEX,GLPK} to CXXFLAGS
- removed the checking of LpSkeleton from lp_test.cc, because it is an
abstract base class now
- removed unnecessary LDFLAGS when linking with libemon.la

 /*!

 \page undir_graphs Undirected graph structures

 The primary data structures of LEMON are the graph classes.

 Under construction.

 */