* Examples: use .texture of input render targets.

* Assign null instead of undefined.

* fix bug where gammaInput/gammaOutput were reset by the PMREM generators.

# Conflicts:
#	examples/js/pmrem/PMREMCubeUVPacker.js

* propagate encodings properly between PMREM CubeUVPacker and PMREMGenerator as well as through texture constructors.

# Conflicts:
#	examples/js/pmrem/PMREMCubeUVPacker.js

* turn off tonemapping, fix None HDR map option.

# Conflicts:
#	examples/webgl_materials_envmaps_hdr.html

* minor envmaps_hdr improvements.

# Conflicts:
#	examples/webgl_materials_envmaps_hdr.html

* fix double decode.

* recalc materials when changing texture encodings.

# Conflicts:
#	examples/webgl_materials_envmaps_hdr.html

* clean up envmap_hdr example.