When --enable-src is given, the programs in src directory will be
built. If --disable-src is given, those programs will not be built. If
none of them are given, --enable-src is assumed.
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.
Tatsuhiro Tsujikawa