Improve Xcode and CLT config reporting

We support three configurations: Xcode-only, CLT-only, and Xcode with
CLT. Our configuration output should correctly reflect this.

While MacOS::Xcode.version has to continue to return a guess if Xcode is
not installed in order to maintain backwards compatibility, this is an
implementation detail that we don't need to expose to the user. And it
makes `brew --config` output confusing.

So let's only print the "Xcode" line when an actual Xcode installation
is present. This makes it easy to quickly figure out which of the three
possible configurations the user is running.

Addresses #14941, more or less.
mafft: fails with clang

Fixes #16541.
Clojure devel 1.5.0-beta2

Closes #16543.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
tesseract 3.02.02

Closes #16536, because I'm not going to argue about it.
scala --devel 2.10.0-rc5
elasticsearch: persist plugins on upgrade.
jenkins 1.493
pil: Uninstall correctly.

Installs now into the cellar, so that uninstall works.

Closes #16558.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
MacVim 7.3-66

https://github.com/b4winckler/macvim/wiki/ChangeLog

Closes #16561.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
node 0.8.16

Closes #16566.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
sdl_gfx: 2.0.24

Closes #16557.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
jslint4java 2.0.3

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
mu 0.9.9

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
google appengine 1.7.4

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
zebra 2.0.53

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
go-app-engine darwin 386 1.7.4

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
go-app-engine darwin amd64 1.7.4

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
appengine-java-sdk 1.7.4

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
armadillo 3.6.0

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
bogofilter 1.2.3

Signed-off-by: Adam Vandenberg <flangy@gmail.com>