Update spectrum.py to use scipy.linalg
Split matrix conversion functions into new module
Simplify import statements
More efficient to_scipy_sparse_matrix

Doesn't convert to LIL format
Convert laplacian and normalized_laplacian to sparse
Switch adjacency_matrix to sparse
Update incidence_matrix to sparse
Merge branch 'master' into use-sparse-matrix

Resolve conflicts in eigenector.py and katz.py due to switch to sparse matrix in adj_matrix.

Conflicts:
	networkx/algorithms/centrality/eigenvector.py
	networkx/algorithms/centrality/katz.py
Use todense() to match adj_matrix
Use sparse matrix
Directed laplacian to sparse

Mostly done conversion of directed matrix laplacian to sparse matrix format.
The "pagerank" walk is still using dense matrices.
Use spdiags instead of diags

Diags is a new scipy function?  Not found in the version on travis for testing.
Skip tests if no SciPy
More skip tests with SciPy
Git: ignore .class files generated by Jython.
Avoid importing * for relative imports.

This is to prevent Jython from giving the following error:
'import *' not allowed with 'from .'
Don't import Graph Atlas generator if the interpreter is Jython.

The graph_atlas_g function is larger than the maximum method size
limit in Java (64K). This is just a workaround to get networkx to work
with Jython, and obviously it would be preferable to take all of the
Graph Atlas data out of the body of the function, and save it to a
separate data file.
Never import the atlas graph generator by default.

(the docstring for the generators.atlas module already said: "Because
of its size, this module is not imported by default.".)

Also, skip tests involving the graph atlas if running under
Jython. Many other tests still result in a failure or an error with
this interpreter, but at least networkx can be imported.
Merge pull request #1027 from epiasini/add_jython_support

Add basic support for Jython 2.7b1
Merge pull request #1021 from hagberg/use-sparse-matrix

Use sparse matrix