Change the test driver so that simply specifying '-f testclass.testmethod' means that

we want to run just the instance of testclass-testmethod combination and nothing else.

Specifying '-g' now will admit the whole .py test module if it does not contain a matching
testclass-testmethod combination at all.

This option arrangement adheres to the RISC principle of making the common cases fast. :-)

rdar://problem/8584914 Can the default for dotest.py's "-g" flag be switched?

llvm-svn: 118392