Handling the case where the scriptsdir is defined in deployment.xml

When the <scriptsdir> element was defined, it was creating the incorrect
path within the .zpk file.

---- Previous Example 1 ----
deployment.xml:
<scriptsdir>zenddeploymentscripts</scriptsdir>

deployment.properties:
scriptsdir.includes = zenddeploymentscripts/post_stage.php

application.zpk path result:
zenddeploymentscripts/zenddeploymentscripts/post_stage.php

---- Previous Example 2 ----
deployment.xml:
<scriptsdir>zenddeploymentscripts</scriptsdir>

deployment.properties:
scriptsdir.includes = post_stage.php

application.zpk path result:
Errors, saying post_stage.php does not exist

---- After This Commit ----
deployment.xml:
<scriptsdir>zenddeploymentscripts</scriptsdir>

deployment.properties:
scriptsdir.includes = post_stage.php

application.zpk path result:
zenddeploymentscripts/post_stage.php