implement tile sharing for simple maps which use distarray _tile_mapper
add tile_sharing test
Merge branch 'master' of github.com:spartan-array/spartan

Conflicts:
	spartan/expr/transpose.py
add region_map which supports mapping over a region of an array. For
those tiles which are not in the region, reuse the tiles of the original
array.
add a new distributed SVM SDCA algorithm which has good scalability
Merge branch 'master' of github.com:MaggieQi/spartan
add cholesky matrix decomposition
rename disdca_svm
reduce the map operations in each iteration in cholesky
rename SealArray to SealedArray
remove with_array and with_ex parameters from fn_kw of region_map
change comments of fn parameter in region_map
Merge pull request #101 from MaggieQi/cholesky

Add disdca_svm and cholesky into examples