Merge pull request #297 from freec84/add-pet-data-submodule

MRG: added ecat test data set with negative values

I added a ecat7 file with negative values (transmission scan from ecat exac hr+ pet scanner) to the test data.
It seems that alls negative values are set to two times the maximum positive value when read in with nibabel ecat load.

Correct values when loaded are:

min: -0.00061576
max:  0.19215
mean: 0.04933
unit: 1/cm

Author: matthew-brett

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "nibabel-data/nitest-minc2"]
 	path = nibabel-data/nitest-minc2
 	url = git://github.com/matthew-brett/nitest-minc2.git
+[submodule "nipy-ecattest"]
+	path = nibabel-data/nipy-ecattest
+	url = https://github.com/freec84/nipy-ecattest