Environment variables are not resolved in settings files

(Pulled Item 2 of Issue 80 out to this Issue):

when i use a settings file in antlib like in
<property name="gs" value="d:/laglap3/HEAD_CI/tools/maven-2.0.7/conf/settings.xml"/>
<install file="target/xxx.jar" settingsFile="$

">

and, in the settings file, I use a environment variable, like:
<localRepository>$

/mavenrepo</localRepository>

then this environment variable MPA_ROOT is NOT resolved to its value.

Note that this is inconsistent to the behaviour of mvn.bat