Add method "diag" into builtin which is analog to numpy's builtin method [diag].  Associated tests added.
fix als node reuse error in the tiling optimization
add cost_hint for all shuffle exprs
fix some apps, including als, three regression, disdca_svm, cg
fix visit_DotExpr node expr must be a list
fix forest and reshape test
fix concatinate cannot concat two zero-dim array error
fix concatinate error when two arrays are one-dim array
Merge remote-tracking branch 'maggieqi/master'
Merge pull request #194 from MaggieQi/master

fix als node reuse error in the tiling optimization
Merge remote-tracking branch 'upstream/master'
fix itembase_collab, lda, naive_bayes apps
add retile operator
Merge pull request #195 from MaggieQi/master

fix itembase_collab, lda, naive_bayes apps
Merge branch 'master' of git://github.com/GabrielWen/spartan into GabrielWen-master

Conflicts:
	spartan/expr/builtins.py
Merge branch 'GabrielWen-master'
Get workers' log back.
Rewrite fuzzy_kmeans by using built-ins only.
Merge remote-tracking branch 'upstream/master'
Add power API
Merge remote-tracking branch 'upstream/master'
Merge pull request #196 from fegin/master

Get workers' log back
remove some shuffles in the als, naive_bayes