functions.

 - Refined the sparse_to_dense() routines a little.

for zero sized sparse vectors.

commits ago.

vectors of both sparse and dense type.

vector functions.

giving warnings about this I switched to the replacement function
XkbKeycodeToKeysym().

namespace into the normal dlib:: namespace so that code which works
with both sparse and dense vectors is more cohesive.

This change runs into a bug in visual studio 2005 that I can't seem
to find a way to avoid.  Might try it again later, but for now, I'm backing
it out.