support for SCRIPT_NAME for static tag and FileField.url

[Dheerendra Rathor]

By default, static tag just appends STATIC_URL in the path. When running on subpath it results in incorrect static url.

This problem can be solved with appending SCRIPT_NAME in to SCRIPT_URL in settings.py

This can be easily added into default django static tag and django.contrib.staticfiles tag as following:

def render(self, context):
    url = self.url(context)
    # Updating url here with request.META['SCRIPT_NAME'] 
    if self.varname is None:
        return url
    context[self.varname] = url
        return ''

On more research I found that FileSystemStorage and StaticFilesStorage ignores script_name as well.
We might have to do a lot of changes but I think it's worth the efforts.