install pygpu/tests.

but this install them with executable permission.
Fix directory handling in the instruction.
Add pygpu.test()
update doc about pygpu tests.
small changes to comments, messages
Merge pull request #2 from nouiz/master

install pygpu/tests.
Fix completely broken logic about the size of the kernel binary in the cuda backend.
Merge pull request #7 from abergeron/fix_cuda_getbin

Fix completely broken logic about the size of the kernel binary in the cuda backend.