Fix brew update user agent.

This needs to be `Homebrew $HOMEBREW_VERSION` so we can be adequately
filtered.

Closes Homebrew/homebrew#49961.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Library/Homebrew/cmd/update.sh

@@ -342,8 +342,9 @@ EOS
         # (so the API does not return 304: unmodified).
         UPSTREAM_SHA_HTTP_CODE="$(curl --silent '--max-time' 3 \
            --output /dev/null --write-out "%{http_code}" \
-           -H "Accept: application/vnd.github.chitauri-preview+sha" \
+           --user-agent "Homebrew $HOMEBREW_VERSION" \
-           -H "If-None-Match: \"$UPSTREAM_BRANCH_LOCAL_SHA\"" \
+           --header "Accept: application/vnd.github.chitauri-preview+sha" \
+           --header "If-None-Match: \"$UPSTREAM_BRANCH_LOCAL_SHA\"" \
            "https://api.github.com/repos/$UPSTREAM_REPOSITORY/commits/$UPSTREAM_BRANCH")"
         [[ "$UPSTREAM_SHA_HTTP_CODE" = "304" ]] && exit
       fi

Library/Homebrew/global.rb

@@ -12,7 +12,7 @@ require "rbconfig"
 
 ARGV.extend(HomebrewArgvExtension)
 
-HOMEBREW_VERSION = "0.9.5"
+HOMEBREW_VERSION = ENV["HOMEBREW_VERSION"]
 HOMEBREW_WWW = "http://brew.sh"
 
 require "config"

Library/brew.sh

@@ -1,3 +1,5 @@
+HOMEBREW_VERSION="0.9.5"
+
 odie() {
   if [[ -t 2 ]] # check whether stderr is a tty.
   then
@@ -70,6 +72,7 @@ then
   fi
 fi
 
+export HOMEBREW_VERSION
 export HOMEBREW_BREW_FILE
 export HOMEBREW_RUBY_PATH
 export HOMEBREW_PREFIX