make a copy of matrix for destructive operations

this should fix #157
bump version to 1.5.1-SNAPSHOT
workaround for problem with symmetric-matrix
Updated project.clj again
Third time a charm, project.cljs
fix for #160

problem was that B was declared as optional argument, and it was wrapped into seq, not
passed as matrix
Merge branch 'master' of git://github.com/liebke/incanter into leastsquares

Conflicts:
	modules/incanter-core/project.clj
	project.clj