Split a test into smaller cases

Two cases from IDesignTest.testExtendScope were put into their own tests:
testExtendScopeWithNullShouldDoNothing and
testExtendScopeWithSameDesignShouldDoNothing
Fixed a test in IDesignSpaceTest.java

Bugfix:
testNextRestricted made an inclusive comparison with an exclusive
range restriction. Setting the value to 0.1 should have made the
test fail. The comparison is now exclusive.

Cleanup:
Simplified and broke up some boolean expressions.
Also substituted if-clauses followed by fail() with assertTrue().