[analyzer] Don't emit extra context arrow after returning from an inlined call.

In this code

  int getZero() {
    return 0;
  }

  void test() {
    int problem = 1 / getZero(); // expected-warning {{Division by zero}}
  }

we generate these arrows:

    +-----------------+
    |                 v
    int problem = 1 / getZero();
                  ^   |
                  +---+

where the top one represents the control flow up to the first call, and the
bottom one represents the flow to the division.* It turns out, however, that
we were generating the top arrow twice, as if attempting to "set up context"
after we had already returned from the call. This resulted in poor
highlighting in Xcode.

* Arguably the best location for the division is the '/', but that's a
  different problem.

<rdar://problem/13326040>
[analyzer] Show "Returning from ..." note at caller's depth, not callee's.

Before:
  1. Calling 'foo'
    2. Doing something interesting
    3. Returning from 'foo'
  4. Some kind of error here

After:
  1. Calling 'foo'
    2. Doing something interesting
  3. Returning from 'foo'
  4. Some kind of error here

The location of the note is already in the caller, not the callee, so this
just brings the "depth" attribute in line with that.

This only affects plist diagnostic consumers (i.e. Xcode). It's necessary
for Xcode to associate the control flow arrows with the right stack frame.

<rdar://problem/13634363>
[analyzer] Fix grammar in comment.

By Adam Schnitzer!