title: OpenWrt Package Makefile supporting multiple versions
body: <p>Is there a way to have a single openwrt package Makefile support multiple "versions"?</p>
  
  <p>For example, we have the following package "test1" Makefile:</p>
  
  <pre><code>...
  PKG_NAME:=test1
  PKG_VERSION:=1.2
  PKG_RELEASE:=1
  PKG_REV:=4f0c448faacfbcae185631ece73f196dc66851ca
  
  PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_VERSION)
  PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION)-$(PKG_REV).tar.gz
  PKG_SOURCE_URL:=ssh://git@&lt;&gt;:123456/&lt;remote&gt;/test1.git
  PKG_SOURCE_PROTO:=git
  PKG_SOURCE_VERSION:=$(PKG_REV)
  PKG_SOURCE_SUBDIR:=$(PKG_NAME)-$(PKG_VERSION)
  ...
  </code></pre>
  
  <p>And we have a "test2" package which depends on this package:</p>
  
  <pre><code>...
  define Package/$(PKG_NAME)
          SECTION:=net
          CATEGORY:=test
          TITLE:=test2 package depending on test1
          DEPENDS:=test1
  endef
  ...
  </code></pre>
  
  <p>I want to have test1 package support multiple versions, whereas each version sets the PKG_REV hash differently, and a specific version to be "default".
  I want test2 to <em>select</em> a specific version of test1 <em>if</em> test2 is selected in menuconfig.</p>
  
  <p>What is the correct way to do that?</p>