"CSS Cache" building procedure broken: does break URLs

The "CSS Cache" building procedure is broken: it breaks various "base" URLs as
the removal of "../" URL fragments does not use the proper regular expression escaping
for the dots ("."). For instance, for a "base" URL of /org/sr/ this creates a CSS cache
file with CSS "url(...)" constructs now containing broken URLs. The fix is to apply the proper
escaping of the dots in the regex.