Add conflicts_with DSL method

conflicts_with is a thin wrapper around Requirement which simplifies
marking conflicts between formulae.

Closes Homebrew/homebrew#13687.

Signed-off-by: Misty De Meo <mistydemeo@gmail.com>

Formula/mariadb.rb

@@ -1,14 +1,17 @@
 require 'formula'
 
 class Mariadb < Formula
-  # You probably don't want to have this and MySQL's formula linked at the same time
-  # Just saying.
   url 'http://ftp.osuosl.org/pub/mariadb/mariadb-5.3.7/kvm-tarbake-jaunty-x86/mariadb-5.3.7.tar.gz'
   homepage 'http://mariadb.org/'
   sha1 '1ee2ef4895aefabd66b4884c382ba2cd1f7bbe2d'
 
   depends_on 'readline'
 
+  conflicts_with 'mysql',
+    :because => "mariadb and mysql install the same binaries."
+  conflicts_with 'percona-server',
+    :because => "mariadb and percona-server install the same binaries."
+
   fails_with :clang do
     build 318
   end

Formula/mysql.rb

@@ -10,6 +10,11 @@ class Mysql < Formula
   depends_on 'readline'
   depends_on 'pidof'
 
+  conflicts_with 'mariadb',
+    :because => "mysql and mariadb install the same binaries."
+  conflicts_with 'percona-server',
+    :because => "mysql and percona-server install the same binaries."
+
   fails_with :llvm do
     build 2326
     cause "https://github.com/mxcl/homebrew/issues/issue/144"

Formula/par2.rb

@@ -5,6 +5,9 @@ class Par2 < Formula
   url 'http://downloads.sourceforge.net/project/parchive/par2cmdline/0.4/par2cmdline-0.4.tar.gz'
   sha1 '2fcdc932b5d7b4b1c68c4a4ca855ca913d464d2f'
 
+  conflicts_with "par2tbb",
+    :because => "par2 and par2tbb install the same binaries."
+
   def patches
     "http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/app-arch/par2cmdline/files/par2cmdline-0.4-gcc4.patch?revision=1.1"
   end

Formula/par2tbb.rb

@@ -1,12 +1,15 @@
 require 'formula'
 
 class Par2tbb < Formula
-  url 'http://chuchusoft.com/par2_tbb/par2cmdline-0.4-tbb-20100203.tar.gz'
   homepage 'http://chuchusoft.com/par2_tbb/'
-  md5 'b1052a08c3c6eac8a7a0605addb161e7'
+  url 'http://chuchusoft.com/par2_tbb/par2cmdline-0.4-tbb-20100203.tar.gz'
+  sha1 '2fcdc932b5d7b4b1c68c4a4ca855ca913d464d2f'
 
   depends_on 'tbb'
 
+  conficts_with "par2",
+    :because "par2tbb and par2 install the same binaries."
+
   fails_with :clang do
     build 318
   end
@@ -21,11 +24,6 @@ class Par2tbb < Formula
     # but only 10.6+ are available on Xcode4
     inreplace 'Makefile.am', /^.*-mmacosx-version.*$/, ''
 
-    if Formula.factory('par2').installed?
-      opoo "par2tbb conflicts with par2. Your par2 binaries will be overwritten.
-         If this bothers you, you can restore par2 with `brew link par2`."
-    end
-
     host_triplet = MacOS.prefer_64_bit? ? "x86_64-apple-darwin11" : "i686-apple-darwin11"
 
     system "./configure", "--disable-debug", "--disable-dependency-tracking",
@@ -34,12 +32,6 @@ class Par2tbb < Formula
     system "make install"
   end
 
-  def caveats
-    <<-EOS.undent
-    par2tbb is a modified fork of par2 and conflicts with its binaries.
-    EOS
-  end
-
   def test
     system "#{bin}/par2"
   end

Formula/percona-server.rb

@@ -6,12 +6,15 @@ class PerconaServer < Formula
   version '5.5.25-27.1'
   sha1 'f3388960311b159e46efd305ecdeb806fe2c7fdc'
 
-  keg_only "This brew conflicts with 'mysql'. It's safe to `brew link` if you haven't installed 'mysql'"
-
   depends_on 'cmake' => :build
   depends_on 'readline'
   depends_on 'pidof'
 
+  conflicts_with 'mysql',
+    :because => "percona-server and mysql install the same binaries."
+  conflicts_with 'mariadb',
+    :because => "percona-server and mariadb install the same binaries."
+
   skip_clean :all # So "INSTALL PLUGIN" can work.
 
   fails_with :llvm do

Formula/rarian.rb

@@ -5,12 +5,10 @@ class Rarian < Formula
   url 'http://rarian.freedesktop.org/Releases/rarian-0.8.1.tar.bz2'
   md5 '75091185e13da67a0ff4279de1757b94'
 
-  def install
-    if Formula.factory('scrollkeeper').installed?
-      opoo "rarian conflicts with scrollkeeper. Your scrollkeeper binaries will be overwritten.
-         If this bothers you, you can restore scrollkeeper with `brew link scrollkeeper`."
-    end
+  conflicts_with 'scrollkeeper',
+    :because => "rarian and scrollkeeper install the same binaries."
 
+  def install
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}"
     system "make install"

Formula/scrollkeeper.rb

@@ -8,6 +8,9 @@ class Scrollkeeper < Formula
   depends_on 'gettext'
   depends_on 'docbook'
 
+  conflicts_with 'rarian',
+    :because => "scrollkeeper and rarian install the same binaries."
+
   def install
     system "./configure", "--prefix=#{prefix}",
                           "--mandir=#{man}",