Merge branch 'jn/makedepend'

* jn/makedepend: Makefile: clarify definition of TEST_OBJS Makefile: always remove .depend directories on 'make clean' Makefile: tuck away generated makefile fragments in .depend Teach Makefile to check header dependencies Makefile: list standalone program object files in PROGRAM_OBJS Makefile: lazily compute header dependencies Makefile: list generated object files in OBJECTS Makefile: disable default implicit rules Makefile: rearrange dependency rules Makefile: transport.o depends on branch.h now Makefile: drop dependency on $(wildcard */*.h) Makefile: clean up http-walker.o dependency rules Makefile: remove wt-status.h from LIB_H Makefile: make sure test helpers are rebuilt when headers change Makefile: add missing header file dependencies Conflicts: Makefile