Properly mark conflicts between open-mpi, libevent, lcdf-typetools.

Closes Homebrew/homebrew#22376.
Closes Homebrew/homebrew#23621.

Formula/lcdf-typetools.rb

@@ -5,6 +5,8 @@ class LcdfTypetools < Formula
   url 'http://www.lcdf.org/type/lcdf-typetools-2.99.tar.gz'
   sha256 'cbb0ed8c42d078fb216b8f4b8ca7a29e0ad3c1969f580a6f2558c829a472adff'
 
+  conflicts_with 'open-mpi', :because => 'both install same set of binaries.'
+
   def install
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}",

Formula/libevent.rb

@@ -17,6 +17,8 @@ class Libevent < Formula
   option :universal
   option 'enable-manpages', 'Install the libevent manpages (requires doxygen)'
 
+  conflicts_with 'open-mpi', :because => 'both install same set of header files'
+
   fails_with :llvm do
     build 2326
     cause "Undefined symbol '_current_base' reported during linking."

Formula/open-mpi.rb

@@ -9,6 +9,8 @@ class OpenMpi < Formula
   option 'enable-mpi-thread-multiple', 'Enable MPI_THREAD_MULTIPLE'
 
   conflicts_with 'mpich2', :because => 'both install mpi__ compiler wrappers'
+  conflicts_with 'libevent', :because => 'both install same set of header files'
+  conflicts_with 'lcdf-typetools', :because => 'both install same set of binaries.'
 
   depends_on :fortran unless build.include? 'disable-fortran'