Fix tests not finding project base directory 'org.aspectj'

Fix tests not finding project base directory 'org.aspectj'

Several LTW tests using class TestServer failed on my machine because
there was a hard-coded project base directory name 'org.aspectj' in the
class. This class has several other problems, but my quick fix for now -
I did not want to rename my project base directory - was to match on a
regex '(?i)(org[.])?aspectj' now. That also works for my root directory
'AspectJ'.

I also moved the code determining the project dir into a protected
(hence testable) method and added a sanity test case checking if the
directory can be determined. If not, the test will fail with a rather
lengthy warning to developers about the need to have a matching project
root folder.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>