Update HttpHeaders.getAccept method

Some servlet containers (iPlanet) parse the Accept header and return
multiple values from request.getHeader("Accept"). The HttpHeaders
getAccept method has been updated to accommodate that hopefully
without causing any other issues.

The extra functionality is in effect only if we find only one
MediaType and there is more than one value for the 'Accept' header.

Issue: SPR-9655
Fix exception message about producible media types

Issue: SPR-10175
Backport "Use ExtendedBeanInfo on an as-needed basis only"

Prior to this change, CachedIntrospectionResults delegated to
ExtendedBeanInfo by default in order to inspect JavaBean
PropertyDescriptor information for bean classes.

Originally introduced with SPR-8079, ExtendedBeanInfo was designed to
go beyond the capabilities of the default JavaBeans Introspector in
order to support non-void returning setter methods, principally to
support use of builder-style APIs within Spring XML. This is a complex
affair, and the non-trivial logic in ExtendedBeanInfo has led to various
bugs including regressions for bean classes that do not declare
non-void returning setters.

Many of these issues were fixed when overhauling non-void JavaBean write
method support in SPR-10029, however it appears that some extremely
subtle issues may still remain. ExtendedBeanInfo was taken out of use
completely in the 3.2.x line with SPR-9677 and the new BeanInfoFactory
mechanism. This support was not backported to 3.1.x, however, in the
interest of stability.

This commit, then, inlines the conditional logic introduced by
BeanInfoFactory directly into CachedIntrospectionResults. The net effect
is that ExtendedBeanInfo is out of the code path entirely except for
bean classes that actually contain 'candidate' methods, i.e. non-void
and/or static write methods.

This commit also includes the changes made in SPR-10115.

Issue: SPR-9723, SPR-10029, SPR-9677, SPR-8079
Fix NPE in FormHttpMessageConverter

Issue: SPR-10187