static code analysis: performance

cppcheck: performance + variable type

code cleanup: quiet warnings with gcc.

Documentation update pass.

Remove "using namespace" from libcola headers.

warning cleanup (no functional changes) - enclose && / || with brackets to avoid ambiguity. - don't cast from booleans to pointers.

Applying fixes for gcc 4.3 build issues (closes LP: #169115)

Previously graph layout was done using the Kamada-Kawai layout algorithm implemented in Boost. I am replacing this with a custom implementation of a constrained stress-majorization algorithm. The stress-majorization algorithm is more robust and has better convergence characteristics than Kamada-Kawai, and also simple constraints can be placed on node position (for example, to enforce downward-pointing edges, non-overlap constraints, or cluster constraints). Another big advantage is that we no longer need Boost. I've tested the basic functionality, but I have yet to properly handle disconnected graphs or to properly scale the resulting layout. This commit also includes significant refactoring... the quadratic program solver - libvpsc (Variable Placement with Separation Constraints) has been moved to src/libvpsc and the actual graph layout algorithm is in libcola.