Setting the CFBundleVersion in a build phase (Xcode >= 4.2). Voluntarily not using the info.plist prefix because of a dependency problem in Xcode build system.

set_build_version.sh

#!/bin/sh

plbuddy="/usr/libexec/PlistBuddy"
toolsdir=$( dirname "${BASH_SOURCE[0]}" )
plist="$BUILT_PRODUCTS_DIR/$INFOPLIST_PATH"

vers=`$toolsdir/make_build_version.sh`
vers="$vers"

major=`$plbuddy -c "Print :CFBundleShortVersionString" "$plist"`
major=(`echo $major | tr '.' ' '`)
major=${major[0]}

vers="$major.$vers"

echo "Setting CFBundleVersion to $vers"

/usr/libexec/PlistBuddy -c "Set :CFBundleVersion $vers" "$plist"
/usr/bin/plutil -convert binary1 "$plist"