XWiki does not work on Java 1.4 anymore

There have been some changes lately that caused the build to fail on jdk 1.4:

• the exo jars are build for java5 only. Does the code compile with 1.4?
• the radeox jar has the same problem (my fault), but it can be rebuilt using jdk 1.4
• in a few places (java) the new String.contains (1.5) is used; these can be replaced by indexOf != -1
• in a few places (velocity) String.replace (1.5) is used; these can be changed with replaceAll (since 1.4), or a custom function compatible with older jdk-s
• a ConcurrentHashMap (1.5) is used for fixing a deadlock (there are jars providing this functionality for 1.4)