Allow implicit hooks/middleware to be disabled.

Fixes #1621.
News for 2.4.3.
Revert "Check that exactly one (existing) source file is found per namespace when compiling"

This reverts commit c2cc916dc69161a76365c9e004b25081b2a7d176.
Release 2.4.3
Bump version number up to 2.4.4-SNAPSHOT.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	leiningen-core/pom.xml