Add gitattributes

Details:
--------

Source files with conflicts (marked with "C" in the log below): resolved manually.
Conflicts in nifskope/resources: simply reverted to trunk/resources (in other words, they have been left unchanged).
Skipped files: manually copied with "svn cp" (except for nifskope/kfm.xml, which is a copy of the docsys/kfm.xml).
Missing targets: ignored.
nifskope/widgets/uvedit.cpp: reverted (i.e. no changes); something went wrong during merge, I think nothing was really changed in the file but for some reason svn failed to recognize that and applied the patch wrongly

Compiler fixes:
gl/glnode.cpp:889: tm &Matrix4 ... -> tm Matrix4 = ...

Merge log:
----------

svn merge -r 2124:2522 https://niftools.svn.sf.net/svnroot/niftools/branches/ver_20_1 .

U    docsys/gen_niflib.py
U    docsys/nifxml.py
C    docsys/nif.xml
U    docsys/kfm.xml
A    nifskope/options.h
C    nifskope/nifvalue.cpp
A    nifskope/LICENSE.TXT
U    nifskope/spells/texture.cpp
A    nifskope/spells/headerstring.cpp
U    nifskope/spells/animation.cpp
Skipped 'nifskope/kfm.xml'
U    nifskope/basemodel.cpp
A    nifskope/options.cpp
U    nifskope/nifxml.cpp
U    nifskope/kfmxml.cpp
U    nifskope/nifmodel.h
Skipped 'nifskope/glcontroller.cpp'
U    nifskope/nifvalue.h
Skipped missing target: 'nifskope/gl/options.h'
Skipped missing target: 'nifskope/gl/FurnitureMarkers.h'
Skipped missing target: 'nifskope/gl/options.cpp'
A    nifskope/gl/glmarker.cpp
U    nifskope/gl/glproperty.cpp
U    nifskope/gl/glnode.cpp
A    nifskope/gl/glmarker.h
Skipped 'nifskope/gltex.cpp'
A    nifskope/CHANGELOG.TXT
U    nifskope/widgets/uvedit.cpp
U    nifskope/widgets/valuedit.cpp
U    nifskope/importex/obj.cpp
C    nifskope/resources/button_view_front.png
A    nifskope/resources/img_update.png
C    nifskope/resources/button_view_user.png
C    nifskope/resources/button_view_walk.png
A    nifskope/resources/img_flag.png
C    nifskope/resources/button_view_top.png
C    nifskope/resources/button_view_side.png
A    nifskope/resources/img_link.png
A    nifskope/gllight.cpp
U    nifskope/NifSkope.pro
U    nifskope/nifmodel.cpp

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