Made TypeExtensions to live alone in a file
Looks like Configuration NET45WP8 works

Which means that using this configuration attempts a build for profile
78 (.NET4.5 Windows Store and WP8). Of course it doesn't build at all
right now.
Some more Msbuild hokey-pokey to support more pcl

TypeExtensions are kept double one for 1st profile, one for 2nd, from
here they'll diverge
TypeExtensions error free...

starting to add new meths for the other errors.