Make CssAbsoluteFilter replace src="..." patterns with absolute paths

The workarounds for many CSS3 properties in IE use proprietary "Filter"
expressions. These often need a "src" variable with an image path. For
some reason, that path is intepreted as relative to the HTML file
including the CSS, not the CSS file itself.

This patch makes those paths absolute as well.

compressor/filters/css_default.py

@@ -9,6 +9,7 @@ from compressor.filters import FilterBase, FilterError
 from compressor.utils import staticfiles
 
 URL_PATTERN = re.compile(r'url\(([^\)]+)\)')
+SRC_PATTERN = re.compile(r'src=([\'"])(.+?)\1')
 
 
 class CssAbsoluteFilter(FilterBase):
@@ -36,7 +37,8 @@ class CssAbsoluteFilter(FilterBase):
             self.protocol = '%s/' % '/'.join(parts[:2])
             self.host = parts[2]
         self.directory_name = '/'.join((self.url, os.path.dirname(self.path)))
-        return URL_PATTERN.sub(self.url_converter, self.content)
+        return SRC_PATTERN.sub(self.src_converter,
+            URL_PATTERN.sub(self.url_converter, self.content))
 
     def find(self, basename):
         if settings.DEBUG and basename and staticfiles.finders:
@@ -86,3 +88,13 @@ class CssAbsoluteFilter(FilterBase):
         if self.has_scheme:
             full_url = "%s%s" % (self.protocol, full_url)
         return "url('%s')" % self.add_suffix(full_url)
+
+    def src_converter(self, matchobj):
+        url = matchobj.group(2)
+        url = url.strip(' \'"')
+        if url.startswith(('http://', 'https://', '/', 'data:')):
+            return "src='%s'" % self.add_suffix(url)
+        full_url = posixpath.normpath('/'.join([str(self.directory_name), url]))
+        if self.has_scheme:
+            full_url = "%s%s" % (self.protocol, full_url)
+        return "src='%s'" % self.add_suffix(full_url)