Fix glp_prob definition (#286)

Add a test file for the connectivity functions (#285)
The Euler tools have a separate test file.

Doc improvements and fixes for connectivity tools (#285)
And add loopFree(), parallelFree(), simpleGraph() to the module doc.

Bug fixes in connectivity.h (#285)

- Bug fix in tree().
- Rename simpleDigraph() to simpleGraph() (it works for both
directed and undirected graphs).
- Possibly faster implementation for parallelFree() and
simpleGraph().

Merge

Add the solver libraries to lemon.pc.in (#281)

Merge

Resolve gcc-4.3 warning in lemon/network_simplex.h

Less map copying in NetworkSimplex (#234)

- The graph is copied in the constructor instead of the init() function.
It must not be modified after the class is constructed.
- The maps are copied once (instead of twice).
- Remove FlowMap, PotentialMap typedefs and flowMap(), pontentialMap()
setter functions.
- flowMap() and potentialMap() query functions copy the values into the
given map (reference) instead of returning a const reference to a
previously constructed map.

Rename Flow to Value in the flow algorithms (#266)

We agreed that using Flow for the value type is misleading, since
a flow should be rather a function on the arcs, not a single value.

This patch reverts the changes of [dacc2cee2b4c] for Preflow and
Circulation.