Final patches from ASM 5.0.2 release

Issue: SPR-11212
DispatcherServlet skips multipart resolution if error page exception attribute indicates MultipartException as root cause

Issue: SPR-11716
checkNotModified leniently handles IE-10-style If-Modified-Since values and silently proceeds if header value cannot be parsed at all

Issue: SPR-11727
SpringProperties falls back to ClassLoader.getSystemResource when loaded in bootstrap ClassLoader

Issue: SPR-11721
Polish logging in resource handling
ServletServerHttpResponse specifically checks for Servlet 3.0's HttpServletResponse.getHeader(String) method

Issue: SPR-11712
Polishing
General defensiveness about the bootstrap ClassLoader (i.e. null ClassLoader)

Issue: SPR-11721
Polishing