adding a test to verify that the TextReporter plumbing works.

It just pumps events through the pretty and plain reporters to verify
things don't crash.  Pretty lame, but it's better than nothing.  We'll
add actual verification later.
move FakeFileHandle into its own file.

This is was previously in Reporter+Testing.h
ReportMessage becomes ReportStatusMessage w/ optional begin & end

Sometimes we want to announce the beginning and ending of a long running
task - e.g. collecting build settings via -showBuildSettings, installing
an app in the simulator for app tests, trying to search for a target
via -find-target.

With ReportMessage as it was, to announce the begin and end of
something, we'd have to write multiple lines. e.g. --

```
[Info] Doing some thing...
[Info] Finsihed doing some thing. (100 ms)
```

Instead, we'd prefer to have the "finish" message write over the "begin"
message so that we first see...

```
[Info] Doing some thing...
```

... but when it finishes, the line gets rewritten to be ...

```
[Info] Finsihed doing some thing. (100 ms)
```

This changes ReportMessage() to ReportStatusMessage(), which like the
original, writes 1 line of output via the text reporter.

But, for things that have a begin and end, use
ReportStatusMessageBegin() and ReportStatusMessageEnd().  The former
will write 1 line of output, the latter will rewrite that 1 line of
output.
changing some ReportStatusMessage() calls to use the Begin/End versions.

For the task-oriented call sites of ReportMessageMessage(), let's switch
to using ReportMessageMessageBegin() at the start of the task and
ReportMessageMessageEnd() at the end of the task.

Did some manual testing with -find-target and app test running.
announce that we're collecting build settings when xctool starts.

^^^, and print the duration.  This will save people a lot of confusion -
no one understands what xctool is doing during the long hang before
it starts building/testing.
use a relative path when printing the 'Found target ...' message.

It just makes the output more pleasant.

Tested with...

```
~/xctool/xctool.sh -find-target TestProject-Library-OSXTests build
```
Merge pull request #55 from facebook/fpotter/status-messages

Support for status message events that have a begin and end.