Added Power function and tests.
Moved power function in the right folder.
Fixed error caused by moving the function.
	modified:   ../__init__.py
	modified:   ../extra_ops.py
	modified:   test_extra_ops.py
	new file:   test_fill_diagonal_offset.py
still have bug
gradient still not implemented fot there is an  undefined gradient
Add fill_diagonal_offet()
	deleted:    theano/tensor/tests/test_fill_diagonal_offset.py
delete test_fill_diagonal.py, modify test in to ignore input offset. Test passed
move TypeError into make_node, consequently changed the test a little. Add a note to declarethe difference between fill_diagonal and fill_diagonal_offset
Recover the deleted test_fill_diagonal()
strange that trailc build did not pass, so add a small change and commit again
1.fix typo\n2.move import to the top\n3.replace (1-pos_offset_flag) with neg_offset_flag\n4.replace grad.shape[1] with a.shape[1]\n5.remove axis_grad\n Waited to be done rewrite test_extro_ops]
Forgot to execute a test.It seems that theano.tensor can not be imported from the top of the file. However, functions that I need are in basic.py therefore there's no need to import theano.tensor or anything else.
Added matrix_power function.
Added test to check for wrong shape in power function.
Modify test_fill_diagonal_offset.py to cover every possible case
Merge pull request #1892 from Tanjay94/Power

Power
Merge pull request #1915 from Tanjay94/Matrix_Power

Matrix_power
Style changed.