RF: use catch_warnings for checkwarn module

Simplify code, by not checking if new filters have been loaded on top.

The code was also causing errors in python 3.3 because we weren't
restoring warnings errors correctly.
TST: add python 3.3 travis build
Added MultiframeWrapper class and multiframe dicom check.
frame0 initiated, conversion to float for scaling values
updated image_orient_patient function
few updates to naming conventions for edicom sequences - e.g., PixelMeasuresSequence
instantiate superclass in MultiframeWrapper __init__
added is_edicom flag
fixed sop class comparison
BF: deal with case where DICOM does not have SOP

We don't want to require that DICOMs have SOPClassUID; allow None for
this attribute.
NF: add stripped down DICOM data for test
TST + NF: test for dicomwrappers and raising errors
ENH: Handle 4D+ datasets.
ENH: Improve get_data for 4D+ multiframe

Use pixel_array instead of PixelData so pydicom handles many
complexities. Sorts/reshapes the array in place.
BF+TST: Fixed lookups for iop/ipp/pixspacing
TST: Add test data for previous commit
TST: Point multiframe test at correct file.
TST: Add test that makes sure resulting data order doesn't change for 4D multiframe.
CMP: Fix Python3 incompatability in last commit.
TST: test default wrapper attributes

Test that b_matrix and q_vector are None by default