Merge bmake-20150606

Only change to bmake is man page - document .OBJDIR target.
We also get latest dirdeps.mk and friends.

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_M contrib/bmake
M contrib/bmake/ChangeLog
M contrib/bmake/Makefile
M contrib/bmake/bmake.1
M contrib/bmake/bmake.cat1
M contrib/bmake/make.1
M contrib/bmake/mk/ChangeLog
M contrib/bmake/mk/dirdeps.mk
M contrib/bmake/mk/gendirdeps.mk
M contrib/bmake/mk/install-mk
M contrib/bmake/mk/meta.stage.mk
M contrib/bmake/mk/meta.sys.mk
M contrib/bmake/mk/mkopt.sh
M contrib/bmake/targ.c
M usr.bin/bmake/Makefile