add edge length and fix quality normalization
make components work for meshes with deleted edges
new topological modification functions
RawField: Add copy
Merge branch 'master' of github.com:otherlab/core
SConstruct: Place toplevel include symlinks in core/build/include

This is friendlier than core/../build/include, which breaks if core is
built standalone.
Ignore build/include
separate_edges function
SConstruct: Fix PREFIX
Merge branch 'master' of github.com:otherlab/core
TriangleMesh: Expose sorted_neighbors to python
vector/Frame.py: Work around strange f.r.v = ... bug
Merge branch 'master' into windows