Sparse matrix support

Explanation of tables
*green Function exists in octave 2.0.x
Noted incompatibilities and missing features
+yellow Function exists in matcompat
Author and home for the function.
?orange Function doesn't exist
Explanation of what you can do instead.
xred Function doesn't exist, and no work-around

Paul Kienzle has fake sparse functions using full matrices which are included herein; Kai Habel has a real tridiagonal solver based on LAPACK; Andy Adler has real sparse matrix support via SuperLU.

Generate sparse matrix
xspeye
xsprand
xsprandn
xsprandsym
+spdiagsspecify diagonals
xspconvertread from file

Manipulate sparse matrices
+sparse
+full
+issparse
+spyview layout
?nnz
?find
xnonzeros
xnzmax
xspones
?spfun
xspalloc
xspparms

Reordering
xcolmmd
xsymmmd
xsymrcm
xcolperm
+randperm
Stephen Eglen
xdmperm

Linear algebra
xeigs
xsvds
xluinc
xcholinc
xnormest
xcondest
xsprank

Solving
xpcg
xbicg
xbicgstab
xcgs
xgmres
xqmr