ENV: move to new paths. (#507)

Move some stuff formerly in `Library/ENV` around:
- Move `Library/ENV/$XCODE_VERSION` to `Library/Homebrew/env/super` as they are
  all superenv wrappers and all symlinks to the same version. We never needed
  the "separate shims for separate versions" functionality and it just adds
  confusion.
- Move `Library/ENV/pkgconfig` to `Library/Homebrew/env/pkgconfig` to get more
  things under `Library/Homebrew`
- Move `Library/ENV/scm` to `Library/scm` as these wrappers are not actually
  used by or related to superenv (or stdenv) in any way.

Library/Homebrew/test/lib/config.rb

@@ -12,7 +12,7 @@ TEST_TMPDIR = ENV.fetch("HOMEBREW_TEST_TMPDIR") { |k|
 
 # Paths pointing into the Homebrew code base that persist across test runs
 HOMEBREW_LIBRARY_PATH  = Pathname.new(File.expand_path("../../..", __FILE__))
-HOMEBREW_ENV_PATH      = HOMEBREW_LIBRARY_PATH.parent+"ENV"
+HOMEBREW_SHIMS_PATH    = HOMEBREW_LIBRARY_PATH.parent+"Homebrew/shims"
 HOMEBREW_LOAD_PATH     = [File.expand_path("..", __FILE__), HOMEBREW_LIBRARY_PATH].join(":")
 
 # Paths redirected to a temporary directory and wiped at the end of the test run

Library/Homebrew/utils/git.rb

 module Utils
   def self.git_available?
     return @git if instance_variable_defined?(:@git)
-    @git = quiet_system HOMEBREW_ENV_PATH/"scm/git", "--version"
+    @git = quiet_system HOMEBREW_SHIMS_PATH/"scm/git", "--version"
   end
 
   def self.git_path
     return unless git_available?
     @git_path ||= Utils.popen_read(
-      HOMEBREW_ENV_PATH/"scm/git", "--homebrew=print-path"
+      HOMEBREW_SHIMS_PATH/"scm/git", "--homebrew=print-path"
     ).chuzzle
   end
 
   def self.git_version
     return unless git_available?
     @git_version ||= Utils.popen_read(
-      HOMEBREW_ENV_PATH/"scm/git", "--version"
+      HOMEBREW_SHIMS_PATH/"scm/git", "--version"
     ).chomp[/git version (\d+(?:\.\d+)*)/, 1]
   end
 

Library/brew.rb

@@ -55,7 +55,7 @@ begin
   end
 
   # Add SCM wrappers.
-  ENV["PATH"] += "#{File::PATH_SEPARATOR}#{HOMEBREW_ENV_PATH}/scm"
+  ENV["PATH"] += "#{File::PATH_SEPARATOR}#{HOMEBREW_SHIMS_PATH}/scm"
 
   if cmd
     internal_cmd = require? HOMEBREW_LIBRARY_PATH.join("cmd", cmd)

Library/brew.sh

@@ -29,7 +29,7 @@ brew() {
 }
 
 git() {
-  "$HOMEBREW_LIBRARY/ENV/scm/git" "$@"
+  "$HOMEBREW_LIBRARY/Homebrew/shims/scm/git" "$@"
 }
 
 # Force UTF-8 to avoid encoding issues for users with broken locale settings.