For cpantesters. Rework to pass tests under random dirname.

I found previous approach (Build.PL hook to make sure symlink _build/lib/YATT)
did not work. So, I finally decided to use @INC-hook. (But it's really clumsy!)

Now `prove -r t` should work fine under random dirname.

Note: t/runtests.zsh now skips `samples/**/*.t`. To test them,
we still need to extract dist_root as `lib/YATT`.
Checking in changes prior to tagging of version 0.0_6.

Changelog diff is:

diff --git a/Changes b/Changes
index 99e7288..c020d4e 100644
--- a/Changes
+++ b/Changes
@@ -1,6 +1,6 @@
 Revision history for YATT::Lite

-0.0_5 2013-05-16
+0.0_6 2013-05-17

  * To make sure all tests are runnable for cpantesters.