NF: add iter method to Openers utility class

parrec uses iteration over lines of a text file; implement this in the
Openers wrapper and test.
NF: add PAR / REC data for testing

Thanks Michael H for releasing it.
NF: add skeleton for tests for PAR/REC conversion

Test against values from converted NIfTI header
RF+BF: refactor parrec to use latest nibabel

Adapt to BinOpener fileobj object as input.

Change returned TR value to seconds instead of milliseconds.

Add get_data_offset and get_slope_inter methods for compatibility with
standard ArrayProxy object.

Add option to set default scaling as input to header __init__
TST: add test of parrec2nii script

Use new PAR/REC data and Philips converted nifti image to test against.
RF: change slice orientation names for par/rec

Change 'transversal' to 'transverse'; 'sagital' to 'sagittal'.  I think
these are the standard names:
http://en.wikipedia.org/wiki/Sagittal_plane