Fix to dwipreproc & phase encode handling
When all DWI volumes are acquired with reversed phase-encoding (i.e. not just b=0 images for estimating the inhomogeneity field), it’s possible to take each pair of DW volumes that have the same diffusion gradient direction, and combine them into a single volume, in a manner that accounts for the differences in information content when the two images are stretched / compressed relative to one another. This is performed when using the -rpe_all option, as well as the -rpe_header option if the input data are appropriate. However my initial testing of this functionality was not thorough enough, and a couple of users have encountered issues. It should hopefully now be working… 
There’s also been corresponding changes to the management of phase encoding information in image headers. Some users may have encountered a warning regarding “invalid phase encoding tables”. While this warning will still occur with existing data, newly-generated images will erase this information when it is no longer relevant such that this warning no longer appears.