the extended file format is still under development and related
libs/binaries are not fit for release
configure:
--enable/disable-libwebpmux; default is disabled.
makefile.unix:
src/mux/libwebpmux.a and examples/webpmux must be explicitly specified
Makefile.vc:
$(DIRLIB)\libwebpmux.lib and $(DIRBIN)\webpmux.exe must be explicitly
specified
Change-Id: I8246746b256010dd2a2e4de58291222d7eaf0457
e41a759615