Don't flush in ErrorPageFilter for < 400 response that's committed

Previously, for a non-async response with a successful status (< 400),
ErrorPageFilter would always call flushBuffer. This triggers an
exception in Tomcat if the client has closed the connection before the
response has been fully sent. In this case, Tomcat treats the response
as successful and commits it before control returns to the filter.

This commit updates ErrorPageFilter to only perform the flush if the
response has not already been committed, leaving any further flushing
that may be necessary to be handled by the servlet container.

Fixes gh-1938
Merge branch '1.1.x'
Omit null pathInfo from ErrorPageFilter's error message

Fixes gh-1944
Merge branch '1.1.x'
Upgrade to Spring Integration 4.0.5.RELEASE

Closes gh-1905
Upgrade to Spring AMQP 1.3.7.RELEASE

Closes gh-1906
Upgrade to Tomcat 7.0.57

Closes gh-1936
Merge branch '1.1.x'

Conflicts:
	spring-boot-dependencies/pom.xml
Use HttpMapper properties only if defined

See gh-1923
Test that HttpMapper properties are only used when they’re defined

Closes gh-1923
Merge branch 'jackson-mapper'
adding test for ssl keystore residing in classpath