In this commit, we made --dep-idle behaviour by default. This is
because the previous default behaviour is not reflect current usage of
dependency priority and never will be because of fragility of tree due
to stream closure.
To distinguish the to-be-installed programs and non-installable
example source code, the former programs, spdycat, spdydyd and shrpx,
were moved to src directory. spdynative was removed from Makefile
because it does not appeal to any users much.