Renamed integrity tests to standard.

Given that the grid will only successfully solve in the first place if
it's valid, playing these down as "integrity" tests when the result
*must* be correct is silly.  Correctness should be explicitly tested
elsewhere, anyway.

diff --git a/pseudoku/tests/integrity/__init__.py b/pseudoku/tests/standard/__init__.py
similarity index 100%
rename from pseudoku/tests/integrity/__init__.py
rename to pseudoku/tests/standard/__init__.py

diff --git a/pseudoku/tests/integrity/simple.py b/pseudoku/tests/standard/simple.py
similarity index 100%
rename from pseudoku/tests/integrity/simple.py
rename to pseudoku/tests/standard/simple.py