Fix command-script-import.test on linux

Fix command-script-import.test on linux

The test was expecting the value of "lldb.frame" to be None, because it
is cleared after each python interpreter session. However, this is not
true in the very first session, because lldb.py sets these values to
invalid objects (lldb.SBFrame(), etc.).

I have not investigated why is it that this test passes on darwin, but
my guess is that this is because we do extra work on darwin (loading the
objc runtime, etc), which causes us to enter the python interpreter
sooner.

This patch changes lldb.py to also initialize these values to None, as
that seems to make more sense. I also fixed some typos in the test while
I was in there.

llvm-svn: 372222